Rna-binding protein

ABSTRACT

A soluble RNA-binding protein having high binding ability is provided. The RNA-binding protein has an amino acid sequence represented by R1′-R1X-R2X-(R5X or R6Y) L -(R5X-R6Y) M -(R5X or R6Y) N -R7X-R8X-R8′, with each symbol meaning a specific amino acid sequence.

CROSS-REFERENCE TO RELAYED APPLICATION

This application is a Continuation of co-pending U.S. patent application Ser. No. 16/494,796, filed Nov. 22, 2019, which is a Section 371 of International Application No. PCT/JP2018/010489, filed Mar. 16, 2018, which was published in the Japanese language on Sep. 20, 2018 under International Publication No. WO 2018/169058 A1, and claims priority under 35 U.S.C. § 119(b) to Japanese Application No. 2017-053093, filed Mar. 17, 2017, the disclosures of which are incorporated herein by reference in their entirety.

REFERENCE TO SEQUENCE LISTING SUBMITTED ELECTRONICALLY

This application contains a sequence listing, which is submitted electronically via EFS-Web as an ASCII formatted sequence listing with a file name “Sequence Listing 688461-23U1”, creation date of Nov. 18, 2021, and having a size of 64,094 bytes. The sequence listing submitted via EFS-Web is part of the specification and is herein incorporated by reference in its entirety.

TECHNICAL FIELD

The present invention relates to an RNA-binding protein.

BACKGROUND ART

A human Pumilio and FBF homology (hPUF) protein is known as an RNA-binding protein having high binding ability and selectivity (see, for example, Non-Patent Document 1). It is known that the hPUF protein has eight repeat motifs that are different in amino acid sequence and length, and three amino acid residues in a single repeat recognize one base. The eight repeat motifs are herein referred to as R1, R2, R3, R4, R5, R6, R7, and R8 from the N-terminal side. The amino acid sequences of the respective repeat motifs are as follows. FIG. 163 shows the regularity of wild-type stacking amino acids by the molecular model.

R1: (SEQ ID NO: 1) HIMEFSQDQHGSRFIQLKLERATPAERQLVFNEILQ R2: (SEQ ID NO: 2) AAYQLMVDVFGNYVIQKFFEFGSLEQKLALAERIRG R3: (SEQ ID NO: 3) HVLSLALQMYGCRVIQKALEFIPSDQQNEMVRELDG R4: (SEQ ID NO: 4) HVLKCVKDQNGNHVVQKCIECVQPQSLQFIIDAFKG R5: (SEQ ID NO: 5) QVFALSTHPYGCRVIQRILEHCLPDQTLPILEELHQ R6: (SEQ ID NO: 6) HIEQLVQDQYGNYVIQHVLEHGRPEDKSKIVAEIRG R7: (SEQ ID NO: 7) NVLVLSQHKFASNVVEKCVTHASRIERAVLIDEVCTMNDGPHS R8: (SEQ ID NO: 8) ALYTMMKDQYANYVVQKMIDVAEPGQRKIVMHKIRP

PRIOR ART DOCUMENTS Non-Patent Documents

-   Non-Patent Document 1: X. Wang, et. al. Cell, Vol. 110, 501-512,     Aug. 23, 2002

SUMMARY OF INVENTION Object to be Solved by the Invention

An object of the present invention is to provide a soluble RNA-binding protein having high binding ability.

Means for Solving the Object

As a result of intensive studies in order to achieve the above objects, the present inventors found that a soluble RNA-binding protein having high binding ability can be designed in accordance with a target RNA sequence by modifying the configuration of eight repeat motifs R1 to R8 or amino acid residues of the motifs. This has led to the completion of the present invention. According to the present invention, the following inventions are provided.

-   <1> An RNA-binding protein having an amino acid sequence represented     by R1′-R1X-R2X-(R5X or R6Y)_(L)-(R5X-R6Y)_(M)-(R5X or     R6Y)_(N)-R7X-R8X-R8′:     wherein -   R1X represents R1, R1(S12N), R1(S12C), R1(Q16E), or R1(Q16R), -   R2X represents R2, R2(N12C), R2(N12S), R2(N12S, Q16E), or R2(N12S,     Q16R), -   R5X represents any one of R5, R5(C12S), R5(C12N), R5(C12S, Q16E), or     R5(C12S, Q16R), -   R6Y represents any one of R6, R6(N12C), R6(N12S), R6(N12S, Q16E), or     R6(N12S, Q16R), -   R7X represents R7, R7(S12C, E16Q), R7(E16Q), R7(S12N, E16Q), or     R7(E16R), -   R8X represents R8, R8(N12C), R8(N12S), R8(N12S, Q16E), or R8(N12S,     Q16R). -   S12N represents a substitution of a 12th amino acid S with N, -   S12C represents a substitution of a 12th amino acid S with C, -   N12C represents a substitution of a 12th amino acid N with C, -   N12S represents a substitution of a 12th amino acid N with S, -   C12N represents a substitution of a 12th amino acid C with N, -   C12S represents a substitution of a 12th amino acid C with S, -   Q16E represents a substitution of a 16th amino acid Q with E, -   Q16R represents a substitution of a 16th amino acid Q with R, -   L and N each independently represent 0 or 1, and M represents an     integer of 2 or more, M preferably represents an integer of 2 to 20,     more preferably an integer of 2 to 10, and even more preferably an     integer of 2 to 5, and -   each repeat corresponds to the following relevant amino acid     sequence:

R1′: (SEQ ID NO: 9) GRSRLLEDFRNNRYPNLQLREIAG; R1: (SEQ ID NO: 1) HIMEFSQDQHGSRFIQLKLERATPAERQLVFNEILQ; R2: (SEQ ID NO: 2) AAYQLMVDVFGNYVIQKFFEFGSLEQKLALAERIRG; R5: (SEQ ID NO: 5) QVFALSTHPYGCRVIQRILEHCLPDQTLPILEELHQ; R6: (SEQ ID NO: 6) HTEQLVQDQYGNYVIQHVLEHGRPEDKSKIVAEIRG; R7: (SEQ ID NO: 7) NVLVLSQHKFASNVVEKCVTHASRIERAVLIDEVCTMNDGPHS; R8: (SEQ ID NO: 8) ALYTMMKDQYANYVVQKMIDVAEPGQRKIVMHKIRP; R8′: (SEQ ID NO: 10) HIATLRKYTYGKHILAKLEKYYMKNGVDLG.

-   <2> The protein according to <1>, wherein for at least one of the     repeats R1X, R2X, R5X, R6Y, R7X, and R8X, -   in a case in which a combination of a base recognized by the repeat     and a downstream base adjacent thereto is A-A, the 13th amino acid     of the corresponding repeat (i.e., an amino acid stacking between     the two bases) is Tyr or His, -   in a case in which the combination is G-A, U-A, C-A, U-C, or C-U,     the 13th amino acid of the corresponding repeat (i.e., an amino acid     stacking between the two bases) is Tyr, -   in a case in which the combination is A-G, A-C, G-U, U-G, C-G, or     G-C, the 13th amino acid of the corresponding repeat (i.e., an amino     acid stacking between the two bases) is Arg, -   in a case in which the combination is A-U or G-G, the 13th amino     acid of the corresponding repeat (i.e., an amino acid stacking     between the two bases) is Arg or His, in a case in which the     combination is U-U, the 13th amino acid of the corresponding repeat     (i.e., an amino acid stacking between the two bases) is Trp or Arg,     and/or -   in a case in which the combination is C-C, the 13th amino acid of     the corresponding repeat (i.e., an amino acid stacking between the     two bases) is Phe. -   <3> An RNA-binding protein having an amino acid sequence represented     by EIRG-(R5X-R6Y)_(n): wherein n R5Xs each independently represent     R5, R5(C12N), R5(C12S, Q16E), or R5(C12S, Q16E), n R6Ys each     independently represent R6, R6(N12C), R6(N12S, Q16E), or R6(N12S,     Q16R), and n represents an integer of 4 to 15:

R5: (SEQ ID NO: 5) QVFALSTHPYGCRVIQRILEHCLPDQTLPILEELHQ; R5(C12N): (SEQ ID NO: 11) QVFALSTHPYGNRVIQRILEHCLPDQTLPILEELHQ; R5(C12S, Q16E): (SEQ ID NO: 12) QVFALSTHPYGSRVIERILEHCLPDQTLPILEELHQ; R5(C12S, Q16R): (SEQ ID NO: 13) QVFALSTHPYGSRVIRRILEHCLPDQTLPILEELHQ; R6: (SEQ ID NO: 6) HTEQLVQDQYGNYVIQHVLEHGRPEDKSKIVAEIRG; R6(N12C): (SEQ ID NO: 14) HTEQLVQDQYGCYVIQHVLEHGRPEDKSKIVAEIRG; R6(N12S, Q16E): (SEQ ID NO: 15) HTEQLVQDQYGSYVIEHVLEHGRPEDKSKIVAEIRG; R6(N12S, Q16R): (SEQ ID NO: 16) HTEQLVQDQYGSYVIRHVLEHGRPEDKSKIVAEIRG.

-   <4> An RNA-binding protein having an amino acid sequence represented     by AFKG-(R5X-R6YZ)_(n-1) R5X-R6Y, wherein n R5Xs each independently     represent R5, R5(C12N), R5(C12S, Q16E), or R5(C12S, Q16E), (n−1)     R6YZs each independently represent R6 (AFKG), R6(N12C) (AFKG),     R6(N12S, Q16E) (AFKG), or R6(N12S, Q16R) (AFKG), R6Y represents R6,     R6(N12C), R6(N12S, Q16E), or R6(N12S, Q16R), and n represents an     integer of 4 to 15:

R5: (SEQ ID NO: 5) QVFALSTHPYGCRVIQRILEHCLPDQTLPILEELHQ; R5(C12N): (SEQ ID NO: 11) QVFALSTHPYGNRVIQRILEHCLPDQTLPILEELHQ; R5(C12S, Q16E): (SEQ ID NO: 12) QVFALSTHPYGSRVIERILEHCLPDQTLPILEELHQ; R5(C12S, Q16R): (SEQ ID NO: 13) QVFALSTHPYGSRVIRRILEHCLPDQTLPILEELHQ; R6(AFKG): (SEQ ID NO: 17) HTEQLVQDQYGNYVIQHVLEHGRPEDKSKIVAAFKG; R6(N12C)(AFKG): (SEQ ID NO: 18) HTEQLVQDQYGCYVIQHVLEHGRPEDKSKIVAAFKG; R6(N12S, Q16E)(AFKG): (SEQ ID NO: 19) HTEQLVQDQYGSYVIEHVLEHGRPEDKSKIVAAFKG; R6(N12S, Q16R)(AFKG): (SEQ ID NO: 20) HTEQLVQDQYGSYVIRHVLEHGRPEDKSKIVAAFKG; R6: (SEQ ID NO: 6) HTEQLVQDQYGNYVIQHVLEHGRPEDKSKIVAEIRG; R6(N12C): (SEQ ID NO: 14) HTEQLVQDQYGCYVIQHVLEHGRPEDKSKIVAEIRG; R6(N12S, Q16E): (SEQ ID NO: 15) HTEQLVQDQYGSYVIEHVLEHGRPEDKSKIVAEIRG; R6(N12S, Q16R): (SEQ ID NO: 16) HTEQLVQDQYGSYVIRHVLEHGRPEDKSKIVAEIRG.

-   <5> The protein according to <3> or <4>, which further has R1′ at     the N terminus and/or R8′ at the C terminus:

R1′: (SEQ ID NO: 9) GRSRLLEDFRNNRYPNLQLREIAG; R8′: (SEQ ID NO: 10) HIATLRKYTYGKHILAKLEKYYMKNGVDLG.

-   <6> The protein according to <3> or <4>, which further has R1′-R1-R2     at the N terminus and/or R8-R8′ at the C terminus.

R1′: (SEQ ID NO: 9) GRSRLLEDFRNNRYPNLQLREIAG; R8′: (SEQ ID NO: 10) HIATLRKYTYGKHILAKLEKYYMKNGVDLG; R1: (SEQ ID NO: 1) HIMEFSQDQHGSRFIQLKLERATPAERQLVFNEILQ; R2: (SEQ ID NO: 2) AAYQLMVDVFGNYVIQKFFEFGSLEQKLALAERIRG; R8: (SEQ ID NO: 8) ALYTMMKDQYANYVVQKMIDVAEPGQRKIVMHKIRP.

-   <A> An RNA-binding protein having an amino acid sequence represented     by -   R1′-R1-R2-R5X-R4-R5X-R6Y-R7-R8-R8′, -   R1′-R1-R2-R3-R6Y-R5X-R6Y-R7-R8-R8′ -   R1′-R1-R2-R5X-R5X-R5X-R6Y-R7-R8-R8′, -   R1′-R1-R2-R5X-R5(R13H)-R5X-R6Y-R7-R8-R8′, -   R1′-R1-R2-R5X-R6Y-R5X-R6Y-R7-R8-R8′, -   R1′-R1-R2-R5X-R6Y-R5X-R6Y-R5X-R6Y-R7-R8-R8′, -   R1′-R1-R2-R3-R4-R5X-R6Y-R7(ILQ)-R8-R8′, -   R1′-R1-R2-R3-R4-R5X-R6Y-R7(IRG)-R8-R8′, -   R1′-R1-R2-R5X-R6Y-R5X-R6Y-R5X-R6Y-R5X-R6Y-R7-R8-R8′, -   R1′-R1-R2-R5X-R6Y-R5X-R6Y-R5X-R6Y-R5X-R6Y-R5X-R6Y-R7-R8-R8′, -   R1′-R1-R2-R5X-R6Y-R5X-R6Y-R5X-R6Y-R5X-R6Y-R5X-R6Y-R5X-R6Y-R7-R8-R8′, -   R1′-R1-R2-R5X-R5X-R5X-R6-R7-R8-R8′, -   R1′-R1-R2-R3-R6Y-R5X-R6Y-R7-R8-R8′ -   R1′-R1-R2-R3-R6Y-R5X-R6Y-R7-R8-R8′ -   R1′-R1-R2-R3-R6Y-R5X-R6Y-R7-R8-R8′ -   R1′-R1-R2-R3-R4-R5 (R13K)-R6Y-R7-R8-R8′, -   R1′-R1-R2-R3-R4-R5X-R6(Y13W)-R7-R8-R8′, -   R1′-R1-R2-R5X-R5(R13H)-R5(R13H)-R6Y-R7-R8-R8′, -   R1′-R1-R2-R5X-R5(R13F)-R5(R13F)-R6Y-R7-R8-R8′, -   R1′-R1-R2-R5X-R5(R13Y)-R5(R13Y)-R6Y-R7-R8-R8′, -   R1′-R1-R2-R5X-R5(R13W)-R5(R13W)-R6Y-R7-R8-R8′, -   R1′-R1-R2-R6Y-R5X-R6Y-R5X-R6Y-R7-R8-R8′, -   R1′-R1-R2-R5X-R5X-R6Y-R5X-R6Y-R7-R8-R8′, -   R1′-R1-R2-R5X-R6Y-R5X-R6Y-R6Y-R7-R8-R8′, -   R1′-R1-R2-R5X-R5X-R6Y-R5X-R6Y-R5X-R6Y-R7-R8-R8′, -   R1′-R1-R2-R5X-R5X-R6Y-R5X-R6Y-R5X-R6Y-R5X-R6Y-R7-R8-R8′, or -   R1′-R1-R2-R5X-R5X-R6Y-R5X-R6Y-R5X-R6Y-R5X-R6Y-R5X-R6Y-R7-R8-R8′     (wherein R5X represents R5, R5(C12N), R5(C12S, Q16E), or R5(C12S,     Q16R), R6Y represents R6, R6(N12C), R6(N12S, Q16E) or R6(N12S,     Q16R), and each repeat corresponds to the following relevant amino     acid sequence):

R1′: (SEQ ID NO: 9) GRSRLLEDFRNNRYPNLQLREIAG; R1: (SEQ ID NO: 1) HIMEFSQDQHGSRFIQLKLERATPAERQLVFNEILQ; R2: (SEQ ID NO: 2) AAYQLMVDVFGNYVIQKFFEFGSLEQKLALAERIRG; R3: (SEQ ID NO: 3) HVLSLALQMYGCRVIQKALEFIPSDQQNEMVRELDG; R4: (SEQ ID NO: 4) HVLKCVKDQNGNHVVQKCIECVQPQSLQFIIDAFKG; R5: (SEQ ID NO: 5) QVFALSTHPYGCRVIQRILEHCLPDQTLPILEELHQ; R5(R13H): (SEQ ID NO: 21) QVFALSTHPYGCHVIQRILEHCLPDQTLPILEELHQ; R5(C12N): (SEQ ID NO: 22) QVFALSTHPYGNRVIQRILEHCLPDQTLPILEELHQ; R5(R13K): (SEQ ID NO: 23) QVFALSTHPYGCKVIQRILEHCLPDQTLPILEELHQ; R5(R13F): (SEQ ID NO: 24) QVFALSTHPYGCFVIQRILEHCLPDQTLPILEELHQ; R5(R13Y): (SEQ ID NO: 25) QVFALSTHPYGCYVIQRILEHCLPDQTLPILEELHQ; R5(R13W): (SEQ ID NO: 26) QVFALSTHPYGCWVIQRILEHCLPDQTLPILEELHQ; R5(C12S, Q16E): (SEQ ID NO: 12) QVFALSTHPYGSRVIERILEHCLPDQTLPILEELHQ; R5(C12S, Q16R): (SEQ ID NO: 13) QVFALSTHPYGSRVIRRILEHCLPDQTLPILEELHQ; R6: (SEQ ID NO: 6) HTEQLVQDQYGNYVIQHVLEHGRPEDKSKIVAEIRG; R6(N12C): (SEQ ID NO: 14) HTEQLVQDQYGCYVIQHVLEHGRPEDKSKIVAEIRG; R6(N12S, Q16E): (SEQ ID NO: 15) HTEQLVQDQYGSYVIEHVLEHGRPEDKSKIVAEIRG; R6(N12S, Q16R): (SEQ ID NO: 16) HTEQLVQDQYGSYVIRHVLEHGRPEDKSKIVAEIRG; R6(Y13W): (SEQ ID NO: 27) HTEQLVQDQYGNWVIQHVLEHGRPEDKSKIVAEIRG; R7: (SEQ ID NO: 7) NVLVLSQHKFASNVVEKCVTHASRTERAVLIDEVCTMNDGPHS; R7(ILQ): (SEQ ID NO: 28) NVLVLSQHKFASNVVEKCVTHASRTERAVLIDEILQ; R7(IRG): (SEQ ID NO: 29) NVLVLSQHKFASNVVEKCVTHASRTERAVLIDEIRG; R8: (SEQ ID NO: 8) ALYTMMKDQYANYVVQKMIDVAEPGQRKIVMHKIRP; R8′: (SEQ ID NO: 10) HIATLRKYTYGKHILAKLEKYYMKNGVDLG.

-   <B> An RNA-binding protein having an amino acid sequence represented     by R1′-(Rx)_(n)-R8′ (wherein n represents an integer of 8 to 30, Rx     independently represents any repeat of R1, R2, R3, R4, R5X, R6X, R7     or R8, the definitions of R1′, R1, R2, R3, R4, R5X, R6X, R7, R8, and     R8′ are as described in <A>), wherein for at least one of the     repeats, in a case in which a combination of a base recognized by     the repeat and a downstream base adjacent thereto is A-A, the 13th     amino acid of at least one of the repeats is Tyr or His, in a case     in which the combination is G-A, U-A, C-A, U-C, or C-U, the 13th     amino acid of at least one of the repeats is Tyr, in a case in which     the combination is A-G, A-C, G-U, U-G, C-G, or G-C, the 13th amino     acid of at least one of the repeats is Arg, in a case in which the     combination is A-U or G-G, the 13th amino acid of at least one of     the repeats is Arg or His, in a case in which the combination is     U-U, the 13th amino acid of at least one of the repeats is Trp or     Arg, and/or in a case in which the combination is C-C, the 13th     amino acid of at least one of the repeats is Phe. -   <C> An RNA-binding protein having an amino acid sequence represented     by

R1′-R1-R2-R5-R6-R5-R6-R5-R6-R7-R8-R8′ (wherein R1′ represents GRSRLLEDFRNNRYPNLQLREIAG (SEQ ID NO: 9), R8′ represents HIATLRKYTYGKHILAKLE KYYMKNGVDLG (SEQ ID NO: 10), and R1, R2, R5 to R8, R1′, and R8′ each represent any of the following (1) to (9)): (1) R1: (SEQ ID NO: 1) HIMEFSQDQHGSRFIQLKLERATPAERQLVFNEILQ R2: (SEQ ID NO: 2) AAYQLMVDVFGNYVIQKFFEFGSLEQKLALAERIRG R5: (SEQ ID NO: 5) QVFALSTHPYGCRVIQRILEHCLPDQTLPILEELHQ R6: (SEQ ID NO: 6) HTEQLVQDQYGSYVIRHVLEHGRPEDKSKIVAEIRG R5: (SEQ ID NO: 5) QVFALSTHPYGCRVIQRILEHCLPDQTLPILEELHQ R6: (SEQ ID NO: 6) HTEQLVQDQYGSYVIRHVLEHGRPEDKSKIVAEIRG R5: (SEQ ID NO: 5) QVFALSTHPYGCRVIQRILEHCLPDQTLPILEELHQ R6: (SEQ ID NO: 6) HTEQLVQDQYGSYVIRHVLEHGRPEDKSKIVAEIRG R7: (SEQ ID NO: 7) NVLVLSQHKFASNVVEKCVTHASRTERAVLIDEVCTMNDGPHS R8: (SEQ ID NO: 8) ALYTMMKDQYANYVVQKMIDVAEPGQRKIVMHKIRP (2) R1: (SEQ ID NO: 1) HIMEFSQDQHGSRFIQLKLERATPAERQLVFNEILQ R2: (SEQ ID NO: 2) AAYQLMVDVFGNYVIQKFFEFGSLEQKLALAERIRG R5: (SEQ ID NO: 5) QVFALSTHPYGCRVIQRILEHCLPDQTLPILEELHQ R6: (SEQ ID NO: 6) HTEQLVQDQYGSRVIRHVLEHGRPEDKSKIVAEIRG R5: (SEQ ID NO: 5) QVFALSTHPYGCRVIQRILEHCLPDQTLPILEELHQ R6: (SEQ ID NO: 6) HTEQLVQDQYGSRVIRHVLEHGRPEDKSKIVAEIRG R5: (SEQ ID NO: 5) QVFALSTHPYGCRVIQRILEHCLPDQTLPILEELHQ R6: (SEQ ID NO: 6) HTEQLVQDQYGSRVIRHVLEHGRPEDKSKIVAEIRG R7: (SEQ ID NO: 7) NVLVLSQHKFASNVVEKCVTHASRTERAVLIDEVCTMNDGPHS R8: (SEQ ID NO: 8) ALYTMMKDQYANYVVQKMIDVAEPGQRKIVMHKIRP (3) R1: (SEQ ID NO: 1) HIMEFSQDQHGSRFIQLKLERATPAERQLVFNEILQ R2: (SEQ ID NO: 2) AAYQLMVDVFGNYVIQKFFEFGSLEQKLALAERIRG R5: (SEQ ID NO: 5) QVFALSTHPYGCRVIQRILEHCLPDQTLPILEELHQ R6: (SEQ ID NO: 6) HTEQLVQDQYGSYVIRHVLEHGRPEDKSKIVAEIRG R5: (SEQ ID NO: 5) QVFALSTHPYGCYVIQRILEHCLPDQTLPILEELHQ R6: (SEQ ID NO: 6) HTEQLVQDQYGSYVIRHVLEHGRPEDKSKIVAEIRG R5: (SEQ ID NO: 5) QVFALSTHPYGCYVIQRILEHCLPDQTLPILEELHQ R6: (SEQ ID NO: 6) HTEQLVQDQYGSYVIRHVLEHGRPEDKSKIVAEIRG R7: (SEQ ID NO: 7) NVLVLSQHKFASNVVEKCVTHASRTERAVLIDEVCTMNDGPHS R8: (SEQ ID NO: 8) ALYTMMKDQYANYVVQKMIDVAEPGQRKIVMHKIRP (4) R1: (SEQ ID NO: 1) HIMEFSQDQHGSRFIQLKLERATPAERQLVFNEILQ R2: (SEQ ID NO: 2) AAYQLMVDVFGNYVIQKFFEFGSLEQKLALAERIRG R5: (SEQ ID NO: 5) QVFALSTHPYGCRVIQRILEHCLPDQTLPILEELHQ R6: (SEQ ID NO: 6) HTEQLVQDQYGSYVIEHVLEHGRPEDKSKIVAEIRG R5: (SEQ ID NO: 5) QVFALSTHPYGCRVIQRILEHCLPDQTLPILEELHQ R6: (SEQ ID NO: 6) HTEQLVQDQYGSYVIEHVLEHGRPEDKSKIVAEIRG R5: (SEQ ID NO: 5) QVFALSTHPYGCRVIQRILEHCLPDQTLPILEELHQ R6: (SEQ ID NO: 6) HTEQLVQDQYGSYVIEHVLEHGRPEDKSKIVAEIRG R7: (SEQ ID NO: 7) NVLVLSQHKFASNVVEKCVTHASRTERAVLIDEVCTMNDGPHS R8: (SEQ ID NO: 8) ALYTMMKDQYANYVVQKMIDVAEPGQRKIVMHKIRP (5) R1: (SEQ ID NO: 1) HIMEFSQDQHGSRFIQLKLERATPAERQLVFNEILQ R2: (SEQ ID NO: 2) AAYQLMVDVFGNYVIQKFFEFGSLEQKLALAERIRG R5: (SEQ ID NO: 5) QVFALSTHPYGCRVIQRILEHCLPDQTLPILEELHQ R6: (SEQ ID NO: 6) HTEQLVQDQYGSRVIEHVLEHGRPEDKSKIVAEIRG R5: (SEQ ID NO: 5) QVFALSTHPYGCRVIQRILEHCLPDQTLPILEELHQ R6: (SEQ ID NO: 6) HTEQLVQDQYGSRVIEHVLEHGRPEDKSKIVAEIRG R5: (SEQ ID NO: 5) QVFALSTHPYGCRVIQRILEHCLPDQTLPILEELHQ R6: (SEQ ID NO: 6) HTEQLVQDQYGSRVIEHVLEHGRPEDKSKIVAEIRG R7: (SEQ ID NO: 7) NVLVLSQHKFASNVVEKCVTHASRTERAVLIDEVCTMNDGPHS R8: (SEQ ID NO: 8) ALYTMMKDQYANYVVQKMIDVAEPGQRKIVMHKIRP (6) R1: (SEQ ID NO: 1) HIMEFSQDQHGSRFIQLKLERATPAERQLVFNEILQ R2: (SEQ ID NO: 2) AAYQLMVDVFGNYVIQKFFEFGSLEQKLALAERIRG R5: (SEQ ID NO: 5) QVFALSTHPYGCRVIQRILEHCLPDQTLPILEELHQ R6: (SEQ ID NO: 6) HTEQLVQDQYGSYVIEHVLEHGRPEDKSKIVAEIRG R5: (SEQ ID NO: 5) QVFALSTHPYGCYVIQRILEHCLPDQTLPILEELHQ R6: (SEQ ID NO: 6) HTEQLVQDQYGSYVIEHVLEHGRPEDKSKIVAEIRG R5: (SEQ ID NO: 5) QVFALSTHPYGCYVIQRILEHCLPDQTLPILEELHQ R6: (SEQ ID NO: 6) HTEQLVQDQYGSYVIEHVLEHGRPEDKSKIVAEIRG R7: (SEQ ID NO: 7) NVLVLSQHKFASNVVEKCVTHASRTERAVLIDEVCTMNDGPHS R8: (SEQ ID NO: 8) ALYTMMKDQYANYVVQKMIDVAEPGQRKIVMHKIRP (7) R1: (SEQ ID NO: 1) HIMEFSQDQHGSRFIQLKLERATPAERQLVFNEILQ R2: (SEQ ID NO: 2) AAYQLMVDVFGNYVIQKFFEFGSLEQKLALAERIRG R5: (SEQ ID NO: 5) QVFALSTHPYGSRVIERILEHCLPDQTLPILEELHQ R6: (SEQ ID NO: 6) HTEQLVQDQYGNYVIQHVLEHGRPEDKSKIVAEIRG R5: (SEQ ID NO: 5) QVFALSTHPYGSRVIERILEHCLPDQTLPILEELHQ R6: (SEQ ID NO: 6) HTEQLVQDQYGNYVIQHVLEHGRPEDKSKIVAEIRG R5: (SEQ ID NO: 5) QVFALSTHPYGSRVIERILEHCLPDQTLPILEELHQ R6: (SEQ ID NO: 6) HTEQLVQDQYGNYVIQHVLEHGRPEDKSKIVAEIRG R7: (SEQ ID NO: 7) NVLVLSQHKFASNVVEKCVTHASRTERAVLIDEVCTMNDGPHS R8: (SEQ ID NO: 8) ALYTMMKDQYANYVVQKMIDVAEPGQRKIVMHKIRP (8) R1: (SEQ ID NO: 1) HIMEFSQDQHGSRFIQLKLERATPAERQLVFNEILQ R2: (SEQ ID NO: 2) AAYQLMVDVFGNYVIQKFFEFGSLEQKLALAERIRG R5: (SEQ ID NO: 5) QVFALSTHPYGSRVIERILEHCLPDQTLPILEELHQ R6: (SEQ ID NO: 6) HTEQLVQDQYGNRVIQHVLEHGRPEDKSKIVAEIRG R5: (SEQ ID NO: 5) QVFALSTHPYGSRVIERILEHCLPDQTLPILEELHQ R6: (SEQ ID NO: 6) HTEQLVQDQYGNRVIQHVLEHGRPEDKSKIVAEIRG R5: (SEQ ID NO: 5) QVFALSTHPYGSRVIERILEHCLPDQTLPILEELHQ R6: (SEQ ID NO: 6) HTEQLVQDQYGNRVIQHVLEHGRPEDKSKIVAEIRG R7: (SEQ ID NO: 7) NVLVLSQHKFASNVVEKCVTHASRTERAVLIDEVCTMNDGPHS R8: (SEQ ID NO: 8) ALYTMMKDQYANYVVQKMIDVAEPGQRKIVMHKIRP (9) R1: (SEQ ID NO: 1) HIMEFSQDQHGSRFIQLKLERATPAERQLVFNEILQ R2: (SEQ ID NO: 2) AAYQLMVDVFGNYVIQKFFEFGSLEQKLALAERIRG R5: (SEQ ID NO: 5) QVFALSTHPYGSYVIERILEHCLPDQTLPILEELHQ R6: (SEQ ID NO: 6) HTEQLVQDQYGNYVIQHVLEHGRPEDKSKIVAEIRG R5: (SEQ ID NO: 5) QVFALSTHPYGSYVIERILEHCLPDQTLPILEELHQ R6: (SEQ ID NO: 6) HTEQLVQDQYGNYVIQHVLEHGRPEDKSKIVAEIRG R5: (SEQ ID NO: 5) QVFALSTHPYGSYVIERILEHCLPDQTLPILEELHQ R6: (SEQ ID NO: 6) HTEQLVQDQYGNYVIQHVLEHGRPEDKSKIVAEIRG R7: (SEQ ID NO: 7) NVLVLSQHKFASNVVEKCVTHASRTERAVLIDEVCTMNDGPHS R8: (SEQ ID NO: 8) ALYTMMKDQYANYVVQKMIDVAEPGQRKIVMHKIRP

-   <D> An RNA-binding protein having an amino acid sequence represented     by R1′-R1-R2-R5-R6-R5-R6-R7-R8-R8′ (wherein R1′, R8′, and R1 to R8     are the amino acid sequences described below), wherein -   the protein has any of R1(S12N), R1(Q16E), R1(Q16R), R2(N12C),     R2(N12S), R2(N12S, Q16E), R2(N12S, Q16R), R7(S12C, E16Q), R7(E16Q),     R7(S12N, E16Q), R7(E16R), R8(N12C), R8(N12S), R8(N12S, Q16E), and     R8(N12S, Q16R) as a substitution:

R1′: (SEQ ID NO: 9) GRSRLLEDFRNNRYPNLQLREIAG; R8′: (SEQ ID NO: 10) HIATLRKYTYGKHILAKLEKYYMKNGVDLG; R1: (SEQ ID NO: 1) HIMEFSQDQHGSRFIQLKLERATPAERQLVFNEILQ; R2: (SEQ ID NO: 2) AAYQLMVDVFGNYVIQKFFEFGSLEQKLALAERIRG; R5: (SEQ ID NO: 5) QVFALSTHPYGCRVIQRILEHCLPDQTLPILEELHQ; R6: (SEQ ID NO: 6) HTEQLVQDQYGNYVIQHVLEHGRPEDKSKIVAEIRG; R7: (SEQ ID NO: 7) NVLVLSQHKFASNVVEKCVTHASRIERAVLIDEVCTMNDGPHS; R8: (SEQ ID NO: 8) ALYTMMKDQYANYVVQKMIDVAEPGQRKIVMHKIRP.

-   <7> A nucleic acid encoding the RNA-binding protein according to any     one of <1> to <6> and <A> to <D>. -   <8> A recombinant expression vector including the nucleic acid     according to <7>. -   <9> A host cell including the recombinant expression vector     according to <8>.

Advantageous Effects of Invention

According to the present invention, a soluble RNA-binding protein having high binding ability can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an amino acid sequence of RNA-binding protein. (SEQ ID NOS:2-8, 63,64)

FIG. 2 shows an amino acid sequence of RNA-binding protein. (SEQ ID NOS:1-8, 65,66)

FIG. 3 shows a result of gel shift assay.

FIG. 4 shows an amino acid sequence of RNA-binding protein. (SEQ ID NOS:1-8)

FIG. 5 shows a result of measurement of solubility of RNA-binding protein.

FIG. 6 shows a result of measurement of solubility of RNA-binding protein.

FIG. 7 shows a result of gel shift assay.

FIG. 8 shows an amino acid sequence of RNA-binding protein. (SEQ ID NOS:1,2, 5-8, 67)

FIG. 9 shows an amino acid sequence of RNA-binding protein. (SEQ ID NOS:1-3, 6-8, 68)

FIG. 10 shows a result of measurement of solubility of RNA-binding protein.

FIG. 11 shows a result of gel shift assay.

FIG. 12 shows an amino acid sequence of RNA-binding protein. (SEQ ID NOS:1,2, 5-8)

FIG. 13 shows a result of measurement of solubility of RNA-binding protein.

FIG. 14 shows a result of gel shift assay.

FIG. 15 shows an amino acid sequence of RNA-binding protein. (SEQ ID NOS:1,2, 5-8, 69,70)

FIG. 16 shows a result of gel shift assay.

FIG. 17 shows an amino acid sequence of RNA-binding protein. (SEQ ID NOS:1,2, 5-8)

FIG. 18 shows an amino acid sequence of RNA-binding protein. (SEQ ID NOS:1,5, 7, 8)

FIG. 19 shows a result of measurement of solubility of RNA-binding protein.

FIG. 20 shows a result of measurement of solubility of RNA-binding protein.

FIG. 21 shows a result of gel shift assay.

FIG. 22 shows an amino acid sequence of RNA-binding protein. (SEQ ID NOS:1-8,71)

FIG. 23 shows an amino acid sequence of RNA-binding protein. (SEQ ID NOS:1-6, 8, 72)

FIG. 24 shows a result of gel shift assay.

FIG. 25 shows a result of gel shift assay.

FIG. 26 shows an amino acid sequence of RNA-binding protein. (SEQ ID NOS:1-8)

FIG. 27 shows a result of gel shift assay.

FIG. 28 shows an amino acid sequence of RNA-binding protein. (SEQ ID NOS:1,2, 6-8, 73,74)

FIG. 29 shows a result of gel shift assay.

FIG. 30 shows a result of gel shift assay.

FIG. 31 shows an amino acid sequence of RNA-binding protein. (SEQ ID NOS:1,2, 5-8)

FIG. 32 shows a result of gel shift assay.

FIG. 33 shows an amino acid sequence of RNA-binding protein. (SEQ ID NOS:1,2, 5-8)

FIG. 34 shows an amino acid sequence of RNA-binding protein. (SEQ ID NOS:1,2, 5-8)

FIG. 35 shows a result of gel shift assay.

FIG. 36 shows an amino acid sequence of RNA-binding protein. (SEQ ID NOS:1,2, 5-8,75)

FIG. 37 shows an amino acid sequence of RNA-binding protein. (SEQ ID NOS:1,2, 6-8, 76,77)

FIG. 38 shows a result of gel shift assay.

FIG. 39 shows a result of gel shift assay.

FIG. 40 shows an amino acid sequence of RNA-binding protein. (SEQ ID NOS:1-3, 5-8,78)

FIG. 41 shows an amino acid sequence of RNA-binding protein. (SEQ ID NOS:1-3, 5, 7, 8,79, 80)

FIG. 42 shows a result of gel shift assay.

FIG. 43 shows a result of gel shift assay.

FIG. 44 shows an amino acid sequence of RNA-binding protein. (SEQ ID NOS:1-8, 81, 82)

FIG. 45 shows an amino acid sequence of RNA-binding protein. (SEQ ID NOS:1-8, 83, 84)

FIG. 46 shows a result of gel shift assay.

FIG. 47 shows an amino acid sequence of RNA-binding protein. (SEQ ID NOS:1,2,5-8, 85)

FIG. 48 shows an amino acid sequence of RNA-binding protein. (SEQ ID NOS:1,2,5-8, 86,87)

FIG. 49 shows an amino acid sequence of RNA-binding protein. (SEQ ID NOS:1,2,5-8, 88)

FIG. 50 shows a result of gel shift assay.

FIG. 51 shows an amino acid sequence of RNA-binding protein. (SEQ ID NOS:1,2,5-8, 89)

FIG. 52 shows a result of gel shift assay.

FIG. 53 shows an amino acid sequence of RNA-binding protein. (SEQ ID NOS:1,2,7,8, 90-92)

FIG. 54 shows an amino acid sequence of RNA-binding protein. (SEQ ID NOS:1,2,7,8, 90,91,93)

FIG. 55 shows a result of gel shift assay.

FIG. 56 shows an amino acid sequence of RNA-binding protein. (SEQ ID NOS:1,2,7,8, 90,94,95)

FIG. 57 shows an amino acid sequence of RNA-binding protein. (SEQ ID NOS:1,2,7,8, 90,93, 94)

FIG. 58 shows a result of gel shift assay.

FIG. 59 shows an amino acid sequence of RNA-binding protein. (SEQ ID NOS:1,2,7,8, 96-98)

FIG. 60 shows an amino acid sequence of RNA-binding protein. (SEQ ID NOS:1,2,7,8, 90,93,94)

FIG. 61 shows a result of gel shift assay.

FIG. 62 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:5, 6, 99,100)

FIG. 63 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:5, 6, 101)

FIG. 64 shows a result of gel shift assay.

FIG. 65 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,5-8)

FIG. 66 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,5-8)

FIG. 67 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,5-8)

FIG. 68 shows a result of gel shift assay.

FIG. 69 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,5-8)

FIG. 70 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,5-8)

FIG. 71 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,5-8)

FIG. 72 shows a result of gel shift assay.

FIG. 73 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,5-8)

FIG. 74 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:2,5-8, 102)

FIG. 75 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:2,5-8, 103)

FIG. 76 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:2,5-8, 104)

FIG. 77 shows a result of gel shift assay.

FIG. 78 shows a result of gel shift assay.

FIG. 79 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,5-8)

FIG. 80 shows a result of gel shift assay.

FIG. 81 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,5-8)

FIG. 82 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,5-8,105)

FIG. 83 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,5-8,106)

FIG. 84 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,5-8,107)

FIG. 85 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,5-8,108)

FIG. 86 shows a result of gel shift assay.

FIG. 87 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,5-8)

FIG. 88 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,5-8,109)

FIG. 89 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,5-8,110)

FIG. 90 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,5-8,111)

FIG. 91 shows a result of gel shift assay.

FIG. 92 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2, 5-8)

FIG. 93 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,5,6,8,112)

FIG. 94 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,5,6,8,113)

FIG. 95 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,5,6,8,114)

FIG. 96 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,5,6,8,115)

FIG. 97 shows a result of gel shift assay.

FIG. 98 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2, 5-8)

FIG. 99 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,5,6,8,116)

FIG. 100 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,5,6,8,117)

FIG. 101 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,5,6,8,118)

FIG. 102 shows a result of gel shift assay.

FIG. 103 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2, 5-8)

FIG. 104 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,5-7,119)

FIG. 105 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,5-7,120)

FIG. 106 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,5-7,121)

FIG. 107 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,5-7,122)

FIG. 108 shows a result of gel shift assay.

FIG. 109 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2, 5-8)

FIG. 110 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,5-7,123)

FIG. 111 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,5-7,124)

FIG. 112 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,5-7,125)

FIG. 113 shows a result of gel shift assay.

FIG. 114 shows explanation regarding verification of stacking amino acids.

FIG. 115 shows explanation regarding optimization of amino acids.

FIG. 116 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,7,8,126,127)

FIG. 117 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,7,8,128,129)

FIG. 118 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,7,8,130,131,132)

FIG. 119 shows a result of gel shift assay.

FIG. 120 shows explanation regarding optimization of amino acids.

FIG. 121 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,7,8,133,134)

FIG. 122 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,7,8,135,136)

FIG. 123 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,7,8,137-139)

FIG. 124 shows a result of gel shift assay.

FIG. 125 shows explanation regarding optimization of amino acids.

FIG. 126 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,7,8,140,141)

FIG. 127 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,7,8,142,143)

FIG. 128 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,7,8,144-146)

FIG. 129 shows a result of gel shift assay.

FIG. 130 shows explanation regarding verification of stacking amino acids.

FIG. 131 shows explanation regarding optimization of amino acids.

FIG. 132 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,5-8)

FIG. 133 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,5-8,147)

FIG. 134 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,5-8,148)

FIG. 135 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,5-8,149)

FIG. 136 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,5-8,150)

FIG. 137 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,5-8,151)

FIG. 138 shows a result of gel shift assay.

FIG. 139 shows explanation regarding optimization of amino acids.

FIG. 140 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,6-8,152)

FIG. 141 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,6-8,152,153)

FIG. 142 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,6-8,152,154)

FIG. 143 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,6-8,152,155)

FIG. 144 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,6-8,152,156)

FIG. 145 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,6-8,152,157)

FIG. 146 shows a result of gel shift assay.

FIG. 147 shows explanation regarding optimization of amino acids.

FIG. 148 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,6-8,158)

FIG. 149 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,6-8,158,159)

FIG. 150 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,6-8,160)

FIG. 151 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,6-8,158,161)

FIG. 152 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,6-8,158,162)

FIG. 153 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,6-8,163)

FIG. 154 shows a result of gel shift assay.

FIG. 155 shows explanation regarding optimization of amino acids.

FIG. 156 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,6-8,164)

FIG. 157 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,6-8,165)

FIG. 158 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,6-8,166)

FIG. 159 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,6-8,167)

FIG. 160 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,6-8,168)

FIG. 161 shows an amino acid sequence of RNA-binding protein. (SEQ ID NO:1,2,6-8,169)

FIG. 162 shows a result of gel shift assay.

FIG. 164 shows the regularity of wild-type stacking amino acids

EMBODIMENT OF CARRYING OUT THE INVENTION

The RNA-binding protein of the present invention is an RNA-binding protein comprising a plurality of repeat motifs, which has an N-terminal domain bound to the N terminus of the plurality of repeat motifs and a C-terminal domain bound to the C terminus thereof.

The N-terminal domain is referred to as “R1′ domain” and the C-terminal domain is referred to as “R8′ domain.” The amino acid sequence of the R1′ domain and the amino acid sequence of the R8′ domain are as follows.

R1′: (SEQ ID NO: 9) GRSRLLEDFRNNRYPNLQLREIAG R8′: (SEQ ID NO: 10) HIATLRKYTYGKHILAKLEKYYMKNGVDLG;

The following findings were obtained in the Examples of the present invention.

It was found in Example 1 that when Phe, the 5th or 14th amino acid residue of R1, is substituted with Ala, the binding force decreases, and even when Phe, the 18th amino acid residue of R2, is substituted with Ala does not affect the binding force. In other words, it was suggested that Phe, the 5th or 14th amino acid residue of R1, is involved in the interaction between RNA and a protein.

Solubility and binding ability of an RNA-binding protein with a recognition repeat substitution were examined in Example 2.

As a result, an RNA-binding protein having a substitution of R3 with R5 was soluble, and an RNA-binding protein having a substitution of R4 with R6 was also soluble, both of which had binding ability comparable to that of the wild-type protein.

In addition, an RNA-binding protein having a substitution of R3 with R5 and a substitution of R4 with R5 was soluble and had binding ability. An RNA-binding protein having a substitution of R3 with R5 and a substitution of R4 with R5, which was modified to have a substitution of the 13th amino acid residue, Arg, with His, was also found to have binding ability comparable to the above level.

In addition, an RNA-binding protein having a substitution of R3 with R5 and a substitution of R4 with R6 was soluble and had binding ability comparable to that of the wild-type protein.

It was indicated that for R7-R8 binding, the terminal sequence of R7 is preferably ILQ or IRG, and more preferably ILQ.

Binding ability of an RNA-binding protein having extended recognition repeat(s) was examined in Example 3. As a result, it was suggested that high binding ability can be achieved with a plurality of R5-R6 repeats.

An RNA-binding protein with modified recognition specificity for R5 was prepared and the binding ability was examined in Example 4. As a result, it was found that the degree of the binding ability is in the following order: C12N (recognition of U (hereinafter “U recognition”))>C12S, Q16E (recognition of G (hereinafter “G recognition”))>C12S, Q16R (recognition of C (hereinafter “C recognition”))>MT (R3→R5, R4→R5) (recognition of A (hereinafter “A recognition”)).

In addition, an RNA-binding protein with modified recognition specificity for R6 was prepared and the binding ability was examined. As a result, it was indicated that in the cases of G recognition and C recognition, the protein has binding ability comparable to that of the wild-type protein in the case of U recognition.

The optimal amino acid was examined by modifying U-A and A-U stacking amino acids in Example 5. As a result, it was indicated that Arg can be used as a cationic amino acid between A and U (A-U), and Trp, Tyr, Phe, and His can be used as an aromatic amino acid between U and A (U-A).

The optimal amino acid was examined by modifying A-C and C-A stacking amino acids in Example 5. As a result, it was indicated that Tyr is suitable as an aromatic amino acid between C and A (C-A), and Arg is suitable as a cationic amino acid between A and C (A-C).

In addition, it was indicated that Tyr is suitable as an aromatic amino acid between G and A (G-A), and Arg is suitable as a cationic amino acid between A and G (A-G).

In addition, it was indicated that Arg is suitable as a cationic amino acid between U and G (U-G), and Arg is suitable as a cationic amino acid between G and U (G-U).

Between A and A (A-A), binding ability of an aromatic amino acid was stronger than that of an cationic amino acid. Among aromatic amino acids, Tyr and His had high binding ability.

TABLE 1 13^(th) Stacking Amino Acid Between purine and purine A-A A-G G-A Tyr Arg Try His Between Pyrimidine and purine U-A U-G C-A Tyr Arg Tyr Between purine and pyrimidine A-U A-C G-U Arg Arg Arg

The binding ability of an RNA-binding protein with further extended recognition repeats was examined in Example 7. Considering the superiority and inferiority of the binding ability together with the results of Example 3, it was found that the binding force decreases in the following order from (1) to (4).

(1) 12, 13 repeats,

(2) 10, 11, 14 repeats,

(3) 9, 15 repeats, and

(4) WT, 8, 16 repeats.

The binding ability of each RNA-binding protein was examined by changing recognition specificity in Example 8 in the same manner as in Example 4. In particular, the recognition specificity was changed for R1, R2, R7, and R8, and the effects were confirmed by experiments. Based on the experimental results, the RNA recognition specificity of each protein having the corresponding amino acid sequence was clarified, and the order of binding strength was elucidated.

In Example 9, the optimal amino acid was confirmed by modifying each stacking amino acid as in Example 5. Table 2 below shows the results together with the results obtained in Example 5.

TABLE 2 RNA Recognition Code Table 12th & 16th Base Recognition Amino Acids Recognition Recognition Recognition of A of U of G Recognition of C 12C 16Q 12N 16Q 12S 16E 12S 16R 12S 16Q 13th Stacking Amino Acid Between purine and purine A-A A-G G-A G-G Tyr Arg Tyr Arg His His Between Pyrimidine and purine U-A U-G C-A C-G Tyr Arg Tyr Arg Between purine and pyrimidine A-U A-C G-U G-C Arg Arg Arg Arg His Between purine and pyrimidine U-U U-C C-U C-C Trp Tyr Tyr Phe Arg

By utilizing the knowledge of the present invention, it is possible to design an artificial RNA-binding protein that specifically recognizes the RNA virus genome sequence with high affinity.

<Gene Encoding RNA-Binding Protein>

A method for preparing a gene encoding the RNA-binding protein of the present invention is not particularly limited. However, the gene can be prepared by chemical synthesis of a nucleic acid based on the amino acid sequences disclosed herein.

<Solubilization of RNA-Binding Protein>

In order to improve solubilization of an RNA-binding protein, it is possible to fuse a tag protein that is known to promote solubilization. A maltose-binding protein (MBP) or the like can be used as a tag protein.

<Purification of RNA-Binding Protein>

A recombinant expression vector can be prepared by incorporating a nucleic acid encoding an MBP-tagged RNA-binding protein into an expression vector. A recombinant expression vector can be introduced into a host for expression, thereby allowing each protein to be expressed in the host.

(1) Production of Recombinant Expression Vector

A vector into which the nucleic acid encoding the RNA-binding protein of the present invention is inserted is not particularly limited as long as it can be replicated in a host. Examples thereof include plasmid DNA and phage DNA.

Examples of plasmid DNA include Escherichia coli-derived plasmids (e.g., pET System, pRSET, pBR322, pBR325, pUC118, pUC119, pUC18, and pUC19), Bacillus subtilis-derived plasmids (e.g., pUB110 and pTP5), yeast-derived plasmids (e.g., YEp13, YEp24, and YCp50). Examples of phage DNA include λ phages (e.g., Charon4A, Charon21A, EMBL3, EMBL4, λgt10, λgt11, and λZAP). In addition, animal viruses such as retrovirus and vaccinia virus, and insect virus vectors such as baculovirus can be used.

The nucleic acid (DNA) encoding the RNA binding protein can be inserted into a vector by cleaving the nucleic acid encoding the RNA-binding protein with an appropriate restriction enzyme and inserting it into the restriction enzyme site or multicloning site in the vector.

The nucleic acid encoding the RNA-binding protein must be incorporated into a vector so that the function of the gene can be exerted. In other words, the vector of the present invention may optionally include a cis-element such as an enhancer, a splicing signal, a poly A addition signal, a selection marker, a ribosome-binding sequence (SD sequence), and the like, in addition to a promoter and the nucleic acid encoding the RNA-binding protein. Examples of a selection marker include a dihydrofolate reductase gene, an ampicillin resistance gene, and a neomycin resistance gene.

(2) Production of Transformant

The present invention also relates to a host cell (transformant) including the above-described expression vector. A transformant can be obtained by introducing a recombinant expression vector into a host such that a desired gene (i.e., a nucleic acid encoding an RNA-binding protein) can be expressed. The host is not particularly limited as long as the nucleic acid of the present invention can be expressed.

Examples of the host include bacteria belonging to the genus Escherichia (e.g., Escherichia coli), the Genus Bacillus (Bacillus subtilis), the genus Pseudomonas (e.g., Pseudomonas putida), and the genus Rhizobium (e.g., Rhizobium meliloti). The host may be a yeast such as Saccharomyces cerevisiae or Schizosaccharomyces pombe. Further, the host may be an animal cell such as a COS cell or CHO cell or an insect cell of Sf9, Sf21, or the like.

In a case in which a bacterium such as Escherichia coli is designated as a host, it is preferable that the recombinant expression vector of the present invention can replicate autonomously in a bacterium, and at the same time, it is composed of a promoter, a ribosome-binding sequence, a nucleic acid encoding an RNA-binding protein, and a transcription termination sequence. The vector may also include a gene regulating a promoter.

Examples of Escherichia coli include Escherichia coli K12 and DH1, and Bacillus subtilis or the like can be exemplified. Any promoter may be used as long as it can be expressed in a host such as Escherichia coli. For example, Escherichia coli-derived promoters and phage-derived promoters such as a trp promoter, a lac promoter, a PL promoter, and a PR promoter can be used. An artificially designed and modified promoter such as a tac promoter may be used. A method for introducing the recombinant vector into a bacterium is not particularly limited as long as it is a method for introducing DNA into a bacterium. For example, a method using calcium ions, an electroporation method, and the like can be mentioned.

In a case in which a yeast is used as a host, for example, Saccharomyces cerevisiae, Schizosaccharomyces pombe, Pichia pastoris, or the like can be used. In such case, a promoter is not particularly limited as long as it can be expressed in a yeast. Examples thereof include a gal1 promoter, a gal10 promoter, a heat-shock protein promoter, an MFα1 promoter, a PHO5 promoter, a PGK promoter, a GAP promoter, a ADH promoter, and an AOX1 promoter. A method for introducing the recombinant vector into a yeast is not particularly limited as long as it is a method for introducing DNA into a yeast. For example, an electroporation method, a spheroplast method, a lithium acetate method, and the like can be mentioned.

In a case in which animal cells are used as a host, monkey cells such as COS-7 cells and Vero cells, Chinese hamster ovary cells (CHO cells), mouse L cells, rat GH3 cells, human FL cells, and the like are used. An SRα promoter, SV40 promoter, LTR promoter, CMV promoter, or the like may be used as a promoter. In addition, an early gene promoter of human cytomegalovirus or the like may also be used. Examples of a method for introducing the recombinant vector into animal cells include an electroporation method, a calcium phosphate method, and a lipofection method.

In a case in which insect cells are used as a host, Sf9 cells, Sf21 cells, and the like are used. Examples of a method for introducing the recombinant vector into insect cells include a calcium phosphate method, a lipofection method, and an electroporation method.

(3) Production of RNA-Binding Protein

The RNA-binding protein of the present invention can be obtained by culturing the above-described transformant and collecting the protein from the culture product. The term “culture product” means any of cultured cells/cultured bacterial cells or disrupted cells/bacterial cells, in addition to a culture supernatant. A method for culturing the transformant is carried out in accordance with an ordinary method applied for culturing a host.

Each of a natural medium and a synthetic medium may be used as a medium for culturing a transformant obtained using a microorganism such as E. coli or yeast as a host as long as it is a medium which contains a carbon source, a nitrogen source, an inorganic salt, and the like that can be assimilated by the microorganism such that the transformant can be cultured efficiently. Carbohydrates such as glucose, fructose, sucrose, and starch, organic acids such as acetic acid and propionic acid, and alcohols such as ethanol and propanol are used as carbon sources. Ammonium salts of inorganic acids or organic acids such as ammonia, ammonium chloride, ammonium sulfate, ammonium acetate, and ammonium phosphate or other nitrogen-containing compounds, peptone, meat extract, corn steep liquor, and the like are used as nitrogen sources. Potassium phosphate, dipotassium phosphate, magnesium phosphate, magnesium sulfate, sodium chloride, ferrous sulfate, manganese sulfate, copper sulfate, and calcium carbonate are used as inorganic substances.

Culture is usually carried out at 37° C. for 6 to 24 hours under aerobic conditions such as shake culture or aeration and agitation culture. The pH is maintained at 7.0 to 7.5 during the culture period. The pH is adjusted using an inorganic or organic acid, an alkaline solution, or the like. Antibiotics such as ampicillin and tetracycline may be added to the medium as necessary during culture.

When culturing a microorganism transformed with an expression vector using an inducible promoter as a promoter, an inducer may be added to the medium as necessary. For example, when culturing a microorganism transformed with an expression vector using a Lac promoter, isopropyl-β-D-thiogalactopyranoside (IPTG) or the like may be added to the medium, and when culturing a microorganism transformed with an expression vector using a trp promoter, indoleacrylic acid (IAA) or the like may be added to the medium.

A generally used RPMI 1640 medium or DMEM medium, a medium obtained by adding fetal bovine serum or the like to any of these media, or the like is used as a medium for culturing a transformant obtained using animal cells as a host. Culture is usually performed at 37° C. for 1 to 30 days in the presence of 5% CO₂. Antibiotics such as kanamycin and penicillin may be added to the medium as necessary during culture.

After culture, in a case in which the RNA-binding protein of the present invention is produced inside of cells or bacterial cells, the RNA-binding protein is extracted by disrupting the cells or bacterial cells. In addition, in a case in which the RNA-binding protein of the present invention is produced outside of cells or bacterial cells, the culture solution is directly used or the cells or bacterial cells are removed therefrom by centrifugation or the like. Thereafter, the RNA-binding protein of the present invention can be isolated and purified from the culture product by using any one of or an appropriate combination of general biochemical methods used for protein isolation and purification, such as ammonium sulfate precipitation, gel chromatography, ion exchange chromatography, and affinity chromatography.

<Comparison/Evaluation of Binding Ability by Gel Shift Assay>

It is possible to evaluate whether or not the RNA-binding protein of the present invention binds to a target sequence by gel shift assay.

A target RNA probe labeled with Alexa680 with absorption at 680 nm in the far infrared range (final concentration: 0.5 nM) and the RNA-binding protein (final concentration: 10 to 1000 nM) are mixed at 4° C. for 1 hour in a reaction buffer (10 mM Tris-HCl, pH 7.5, 100 mM NaCl, 1 mM EDTA, 1 mM DTT, 10% Glycerol, 0.05% BSA, 0.2 U RNase inhibitor) and then applied to 6% non-denaturing polyacrylamide gel equilibrated with 0.5×TBE buffer (size: 16×16 cm; thickness: 1 mm), followed by electrophoresis in a cold room (4° C.). Each band of RNA can be visualized by terminating electrophoresis when the dye marker flows 3 cm and detecting the fluorescence in the gel taken out from the device while scanning with a far-infrared detector.

EXAMPLES Example 1 Verification of Interaction via Phe (1) Vector Cloning

FIGS. 1 and 2 show the amino acid sequences of hPUF_MT(F856A), MT(F865A), MT(F856A/F865A), and MT(905A). Total synthesis of genes encoding hPUF_MT(F856A), MT(F865A), MT(F856A/F865A), and MT(905A) was carried out. Synthesized genes were cleaved with BsaI and ligated with pET24-MBP(-B)-R1′-MSC-R8′ which was also cleaved with BsaI, thereby constructing expression vectors. pET24-MBP(-B)-R1′-MSC-R8′ is a vector composed of a pET24 vector including a gene encoding a maltose-binding protein (MBP), a gene encoding R1′, a multicloning site, and a gene encoding R8′.

(2) Protein Expression and Purification

Each obtained expression vector was transduced into E. coli BL21 (DE3). Protein expression was induced by performing shake culture in an LB-Kan medium containing 2% glucose until OD₆₀₀ reached a level of about 0.6 to 0.75, followed by shake culture in a 1 mM IPTG-containing LB-Kan medium at 37° C. for 3 h. E. coli was pelleted and suspended in a lysis buffer (25 mM Tris-HCl (pH 8.0), 500 mM NaCl). Each desired protein was adsorbed by performing freeze-thawing and sonication, mixing the centrifuged supernatant with Profinity™ IMAC Ni-Charged Resin (Biorad), followed by rotoring at 4° C. for 10 h. After washing with a buffer containing 25 mM Tris-HCl (pH 8.0) and 500 mM NaCl and then with a buffer containing 25 mM Tris-HCl (pH 8.0), 500 mM NaCl, and 20 mM imidazole, elution was performed with a buffer containing 25 mM Tris-HCl (pH 8.0), 500 mM NaCl, and 150 mM imidazole. The buffer was exchanged to a buffer containing 50 mM Tris-HCl (pH 7.5) and 300 mM NaCl and concentrated by ultrafiltration. The concentrate was mixed with 99.5% glycerol and 1M DTT such that the mixture had a composition of 25 mM Tris-HCl (pH 7.5), 150 mM NaCl, 50% glycerol, and 5 mM DTT, and then, stored at −20° C.

(3) Gel Shift Assay

An RNA probe (OTS-1511) containing a target sequence fluorescence-labeled with Alexa680 at both ends thereof was synthesized.

OTS-1511: (SEQ ID NO: 30) 5′-Alexa680-CCAGAAUUGUAUAUAUUCG-Alexa680-3′ (19 mer)

Each purified protein was diluted to a desired concentration with Binding Buffer, mixed with a binding buffer and Ribonuclease Inhibitor, Cloned (Invitrogen), and then, mixed with the RNA probe at a final concentration of 0.5 nM. A buffer in a binding reaction had a composition of 10% glycerol, 100 mM NaCl, 10 mM Tris-HCl (pH 7.5), 0.05% BSA, Ribonuclease Inhibitor (0.2 U), 1 mM DTT, and 1 mM EDTA. A binding reaction was performed at 4° C. for 30 min. Subsequently, the solution was gently mixed by pipetting. A binding reaction was performed again at 4° C. for 30 min.

The solution obtained after the binding reaction was applied to 6% a non-denaturing polyacrylamide gel, followed by electrophoresis at 4° C. and 200 V. When the electrophoresis marker (2 μL of 6×Dye+10 μL of 1× binding buffer) moved by 0.5 cm, the voltage was changed to 100 V, and electrophoresis was continuously performed until the electrophoresis marker moved by 3 cm. Finally, RNA was detected with Odyssey.

FIG. 3 shows the results.

When Phe856 and Phe865 were each substituted with Ala, the binding force decreased (about 1/10). Substitution of Phe905 with Ala did not significantly affect the binding force.

The degree of contribution to binding force was found to be in the order of Phe856>Phe865>>Phe905.

Example 2 Confirmation of Recognition Repeats Example 2-1 (1) Vector Cloning

FIG. 4 shows the amino acid sequences of hPUF_MT(R3→R5) and MT(R4→R6).

Total synthesis of genes encoding hPUF_MT(R3→R5) and MT(R4→R6) was carried out. Synthesized genes were cleaved with BsaI and ligated with pET24-R1′-MSC-R8′ which was also cleaved with BsaI, thereby constructing expression vectors.

(2) Protein Expression and Purification

Protein expression and purification were performed by the same procedures as in (2) of Example 1. Note that protein expression was induced in a 0.01 mM IPTG-containing LB-Kan medium at 25° C. for 16 h. Rotoring for absorption to the resin was carried out for 8 h. FIGS. 5 and 6 show the results of examining solubility.

(3) Gel Shift Assay

Gel shift assay was performed by the same procedures as in (3) of Example 1

The following RNA probe was used.

OTS-1511: (SEQ ID NO: 30) 5′-Alexa680-CCAGAAUUGUAUAUAUUCG-Alexa680-3′ (19 mer)

FIG. 7 shows the results. Both MT(R3→R5) and MT(R4→R6) were found to have binding force comparable to that of the wild type.

Example 2-2 (1) Vector Cloning

FIGS. 8 and 9 show the amino acid sequences of hPUF_MT(R3→R5, R4→R5), hPUF_MT(R3→R5, R4→R5_R13H), hPUF_MT(R4→R6, R5→R6), and hPUF_MT(R4→R6, R5→R6_Y13R).

Vector cloning was performed by the same procedures as in Example 2-1.

(2) Protein Expression and Purification

Protein expression and purification were performed by the same procedures as in Example 1. Note that protein expression was induced in a 0.01 mM IPTG-containing LB-Kan medium at 30° C. for 7 h. Rotoring for absorption to the resin was carried out for 10 h.

FIG. 10 shows the results of examining solubility.

(3) Gel Shift Assay

Gel shift assay was performed by the same procedures as in Example 1.

-   The following RNA probes were used.

OTS-1511: (SEQ ID NO: 30) 5′-Alexa680-CCAGAAUUGUAUAUAUUCG-Alexa680-3′ (19 mer) (probe for the wild type) OTS-1759: (SEQ ID NO: 31) 5′-Alexa680-CCAGAAUUGUAAAUAUUCG-Alexa680-3′ (19 mer) (hPUF MT(R3→R5, R4→R5),

-   MT (probe for R3→R5, R4→R5_R13H)

FIG. 11 shows the results.

Example 2-3 (1) Vector Cloning

FIG. 12 shows the amino acid sequences of hPUF_MT(R3→R5, R4→R6) and hPUF_MT(1-6-5-6-5-6-7-8).

Vector cloning was performed by the same procedures as in Example 2-1.

(2) Protein Expression and Purification

Protein expression and purification of hPUF_MT(R3→R5, R4→R6) and hPUF_MT(1-6-5-6-5-6-7-8) were performed by the same procedures as in Example 1. Note that protein expression induction was carried out under the following conditions.

-   hPUF_MT(R3→R5, R4→R6): 25° C. for 16 h in a 0.01 mM IPTG-containing     LB-Kan medium -   hPUF_MT(1-6-5-6-5-6-7-8): 37° C. for 3 h in a 1 mM IPTG-containing     LB-Kan medium

Rotoring for absorption to the resin was carried out for 10 h for hPUF_MT(R3→R5, R4→R6) and for 14 h for hPUF_MT(1-6-5-6-5-6-7-8).

Protein expression and purification of hPUF_MT(R4→R6, R5→R6) and hPUF_MT(R4→R6, R5→R6_Y13R) were performed by the following procedures. Each obtained expression vector was transduced into E. coli BL21(DE3)/pKJE7. Protein expression was induced by performing shake culture in an LB-Cm-Kan medium containing 0.5 mg/mL arabinose until OD₆₀₀ reached a level of about 0.4 to 0.8, and IPTG was added to the medium so as to yield a final concentration of 0.1 mM, followed by shake culture the medium at 30° C. for 7 h. E. coli was pelleted and suspended in a lysis buffer (25 mM Tris-HCl (pH 8.0), 500 mM NaCl). Each desired protein was adsorbed by performing freeze-thawing and sonication, mixing the centrifuged supernatant with Profinity™ IMAC Ni-Charged Resin (Biorad), followed by rotoring at 4° C. for 14 h. After washing with a buffer containing 25 mM Tris-HCl (pH 8.0) and 500 mM NaCl and then with a buffer containing 25 mM Tris-HCl (pH 8.0), 500 mM NaCl, and 20 mM imidazole, elution was performed with a buffer containing 25 mM Tris-HCl (pH 8.0), 500 mM NaCl, and 150 mM imidazole. The buffer was exchanged to a buffer containing 50 mM Tris-HCl (pH 7.5) and 300 mM NaCl and concentrated by ultrafiltration. The concentrate was mixed with 99.5% glycerol and 1M DTT such that the mixture had a composition of 25 mM Tris-HCl (pH 7.5), 150 mM NaCl, 50% glycerol, and 5 mM DTT, and then, stored at −20° C.

FIG. 13 shows the results of examining solubility.

(3) Gel Shift Assay

Gel shift assay was performed by the same procedures as in Example 1. Note that as the protein concentration could not be measured for hPUF_MT(R4→R6, R5→R6) and hPUF_MT(R4→R5→R6_Y13R), stock solutions of their purification samples were used without dilution.

The following RNA probes were used.

OTS-1511: (SEQ ID NO: 30) 5′-Alexa680-CCAGAAUUGUAUAUAUUCG-Alexa680-3′ (19 mer) (probe for the wild type, hPUF_MT(R3→R5, R4→R6), MT(1-6-5-6-5-6-7-8)) OTS-1760: (SEQ ID NO: 32) 5′-Alexa680-CCAGAAUUGUUUAUAUUCG-Alexa680-3′ (19 mer) (probe for hPUF_MT(R4→R6, R5→R6), MT(R4→R6, R5→R6_Y13R))

FIG. 14 shows the results. The binding force of hPUF_MT(1-6-5-6-5-6-7-8) was about one-tenth of that of the wild type (Kd: 50 to 10 nM). Electrophoresis of the R6×3 mutant was unsuccessful because of clogging of wells.

Example 2-4 (1) Vector Cloning

FIG. 15 shows the amino acid sequences of hPUF_MT(1-2-5-6-5-6-5_ILQ-8) and hPUF_MT(1-6-5-6-5-6-5-6_IRP).

Vector cloning was performed by the same procedures as in Example 2-1.

(2) Protein Expression and Purification

Protein expression and purification were performed by the same procedures as in Example 1.

-   Note that protein expression induction was carried out under the     following conditions. -   hPUF_MT(1-2-5-6-5-6-5_ILQ-8): 37° C. for 3 h in a 0.1 mM     IPTG-containing LB-Kan medium -   hPUF_MT(1-2-5-6-5-6-5-6_IRP): 37° C. for 3 h in a 0.1 mM     IPTG-containing LB-Kan medium -   Rotoring for absorption to the resin was carried out for 14 h.

(3) Gel Shift Assay

Gel shift assay was performed by the same procedures as in Example 1.

-   The following RNA probes were used.

OTS-1511: (SEQ ID NO: 30) 5′-Alexa680-CCAGAAUUGUAUAUAUUCG-Alexa680-3′ (19 mer) (wild-type probe) (SEQ ID NO: 33) OTS-1754: 5′-Alexa680-CCAGAAUUAUAUAUAUUCG-Alexa680-3′ (19 mer) (probe for hPUF_MT(1-2-5-6-5-6-5_ILQ-8), MT(1-2-5-6-5-6-5-6_IRP))

FIG. 16 shows the results.

MT(1-2-5-6-5-6-5_ILQ-8) and MT(1-2-5-6-5-6-5-6_IRP) are thought to have binding force weaker than that of the wild type (WT).

Example 2-5 (1) Vector Cloning

FIGS. 17 and 18 h show the amino acid sequences of PUF_MT(1-5-5-5-5-6-7-8), hPUF_MT(1-2-5-6-5-6-5-6-7-8), and hPUF_MT(1-5-5-5-5-5-7-8).

Vector cloning was performed by the same procedures as in Example 2-1.

(2) Protein Expression and Purification

Protein expression and purification were performed by the same procedures as in Example 1.

-   Note that protein expression induction was carried out under the     following conditions. -   hPUF_MT(1-5-5-5-5-6-7-8): 20° C. for 24 h in a 1 mM IPTG-containing     LB-Kan medium -   hPUF_MT(1-2-5-6-5-6-5-6-7-8): 37° C. for 3 h in a 1 mM     IPTG-containing LB-Kan medium -   Rotoring for absorption to the resin was carried out for 10 h.

FIGS. 19 and 20 show the results of examining solubility.

(3) Gel Shift Assay

Gel shift assay was performed by the same procedures as in Example 1.

-   The following RNA probes were used.

OTS-1511: (SEQ ID NO: 30) 5′-Alexa680-CCAGAAUUGUAUAUAUUCG-Alexa680-3′ (19 mer) (probe for the wild type) OTS-1818: (SEQ ID NO: 34) 5′-Alexa680-CCAGAAUUGUAAAAAUUCG-Alexa680-3′ (19 mer) (probe for hPUF_MT(1-5-5-5-5-6-7-8)) OTS-1844: (SEQ ID NO: 35) 5′-Alexa680-CCAGAAUUGUAUAUAUAUUCG-Alexa680-3′ (21 mer) (probe for hPUF_MT(1-2-5-6-5-6-5-6-7-8))

FIG. 21 shows the results. It was found that MT(1-5-5-5-5-6-7-8) has binding force weaker than that of WT, and MT(1-2-5-6-5-6-5-6-7-8) has binding ability almost comparable to that of WT.

Example 2-6 (1) Vector Cloning

FIGS. 22 and 23 show the amino acid sequences of hPUF_MT(R7→R5), hPUF_MT(R7_ILQ), and hPUF_MT(R7_IRG).

Vector cloning was performed by the same procedures as in Example 2-1.

(2) Protein Expression and Purification

Protein expression and purification were performed by the same procedures as in Example 1. Note that protein expression induction was carried out under the following conditions.

-   hPUF_MT(R7→R5): 25° C. for 16 h in a 0.01 mM IPTG-containing LB-Kan     medium -   hPUF_MT(R7_IRG): 25° C. for 16 h in a 0.01 mM IPTG-containing LB-Kan     medium -   hPUF_MT(R7_ILQ): 25° C. for 13 h in a 1 mM IPTG-containing LB-Kan     medium -   Rotoring for absorption to the resin was carried out for 13 h.

(3) Gel Shift Assay

Gel shift assay was performed by the same procedures as in Example 1.

-   The following RNA probes were used.

OTS-1511: (SEQ ID NO: 30) 5′-Alexa680-CCAGAAUUGUAUAUAUUCG-Alexa680-3′ (19 mer) (probe for the wild type, hPUF_MT(R7_ILQ), MT(R7_IRG)) OTS-1754: (SEQ ID NO: 33) 5′-Alexa680-CCAGAAUUAUAUAUAUUCG-Alexa680-3′ (19 mer) (probe for hPUF_MT(R7→R5))

FIG. 24 shows the results. MT(R7→R5) has binding force weaker than that of WT, and the position of the shifted band is higher than expected. MT(R7_ILQ) and MT(R7_IRG) had binding force almost comparable to that of WT.

Example 2-7 (1) Vector Cloning

The same vector as in Example 2-6 was used.

(2) Protein Expression and Purification

Protein expression and purification were performed by the same procedures as in Example 2-6.

(3) Gel Shift Assay

Gel shift assay was performed by the same procedures as in Example 1. The following RNA probe was used.

OTS-1511: (SEQ ID NO: 30) 5′-Alexa680-CCAGAAUUGUAUAUAUUCG-Alexa680-3′ (19 mer)

FIG. 25 shows the results. It is understood that ILQ is a terminal sequence suitable for R7-R8 ligation.

Example 2-8 (1) Vector Cloning

FIG. 26 shows the amino acid sequences of hPUF_MT(R7→R5) and hPUF_MT(R8→R5).

Vector cloning was performed by the same procedures as in Example 2-1.

(2) Protein Expression and Purification

Protein expression and purification were performed by the same procedures as in Example 1.

Note that protein expression was induced in a 1 mM IPTG-containing LB-Kan medium at 37° C. for 3 h.

Rotoring for absorption to the resin was carried out for 8 h.

(3) Gel Shift Assay

Gel shift assay was performed by the same procedures as in Example 1.

The following RNA probes were used.

OTS-1511: (SEQ ID NO: 30) 5′-Alexa680-CCAGAAUUGUAUAUAUUCG-Alexa680-3′ (19 mer) (probe for the wild type, hPUF_MT(R7→ILQ), MT(R7→IRG)) OTS-1754: (SEQ ID NO: 33) 5′-Alexa680-CCAGAAUUAUAUAUAUUCG-Alexa680-3′ (19 mer) (probe for hPUF_MT(R7R5)) OTS-1825: (SEQ ID NO: 36) 5′-Alexa680-CCAGAAUAGUAUAUAUUCG-Alexa680-3′ (19 mer) (probe for hPUF_MT(R8→R5))

FIG. 27 shows the results. MT(R7→R5) has binding force that is significantly weaker than that of WT, and MT(R8→R5) is thought to have substantially no binding ability.

Example 2-9 (1) Vector Cloning

FIG. 28 shows the amino acid sequences of hPUF_MT(R3→RC, R4→RC, R5→RC) and hPUF_MT(R3→RC2, R4→RC2, R5→RC2).

Vector cloning was performed by the same procedures as in Example 2-1.

(2) Protein Expression and Purification

Protein expression and purification were performed by the same procedures as in Example 1.

Note that protein expression induction was carried out under the following conditions.

-   hPUF_MT(R3→RC,R4→RC, R5→RC): 37° C. for 3 h in a 1 mM     IPTG-containing LB-Kan medium -   hPUF_MT(R3RC2,R4RC2,R5RC2): 37° C. for 3 h in a 1 mM IPTG-containing     LB-Kan medium -   Rotoring for absorption to the resin was carried out for 9 h.

(3) Gel Shift Assay

Gel shift assay was performed by the same procedures as in Example 1.

The following RNA probe was used.

OTS-1759: (SEQ ID NO: 31) 5′-Alexa680-CCAGAAUUGUAAAUAUUCG-Alexa680-3′ (19 mer)

FIG. 29 shows the results.

MT(R3→RC,R4→RC, R5→RC) and MT(R3→RC2,R4→RC2,R5→RC2) may have binding force weaker than that of MT(R3→R5, R4→R5).

Example 3 Extension of Recognition Repeats Example 3-1

Vector cloning and protein expression and purification were performed as in Example 2-5.

Gel shift assay was performed by the same procedures as in Example 1.

The following RNA probes were used.

OTS-1511: (SEQ ID NO: 30) 5′-Alexa680-CCAGAAUUGUAUAUAUUCG-Alexa680-3′ (19 mer) (probe for the wild type) OTS-1844: (SEQ ID NO: 35) 5′-Alexa680-CCAGAAUUGUAUAUAUAUUCG-Alexa680-3′ (21 mer) (probe for hPUF_MT(1-2-5-6-5-6-5-6-7-8))

FIG. 30 shows the results. It is understood that MT(1-2-5-6-5-6-5-6-7-8) has binding force about 10 times greater than that of WT.

Example 3-2 (1) Vector Cloning

FIG. 31 shows the amino acid sequence of hPUF_MT(1-2-5-6-5-6-5-6-5-6-7-8).

Vector cloning was performed by the same procedures as in Example 2-1.

(2) Protein Expression and Purification

Protein expression and purification of hPUF_MT(1-2-5-6-5-6-5-6-5-6-7-8) were performed by the same procedures as in Example 1.

Note that protein expression was induced in a 1 mM IPTG-containing LB-Kan medium at 37° C. for 3 h.

-   Rotoring for absorption to the resin was carried out for 12.5 h.

(3) Gel Shift Assay

Gel shift assay was performed by the same procedures as in Example 1.

-   The following RNA probes were used.

OTS-1511: (SEQ ID NO: 30) 5′-Alexa680-CCAGAAUUGUAUAUAUUCG-Alexa680-3′ (19 mer) (probe for the wild type) OTS-1844: (SEQ ID NO: 35) 5′-Alexa680-CCAGAAUUGUAUAUAUAUUCG-Alexa680-3′ (21 mer) (probe for hPUF_MT(1-2-5-6-5-6-5-6-7-8)) OTS-1924: (SEQ ID NO: 37) 5′-Alexa680-CCAGAAUUGUAUAUAUAUAUUCG-Alexa680-3′ (23 mer) (probe for hPUF_MT(1-2-5-6-5-6-5-6-5-6-7-8))

FIG. 32 shows the results. It is understood that MT(1-2-5-6-5-6-5-6-5-6-7-8) and MT(1-2-5-6-5-6-5-6-7-8) have binding ability greater than that of MT(R3→R5, R4→R6).

Example 3-3 (1) Vector Cloning

FIGS. 33 and 34 show the amino acid sequences of hPUF_MT(1-2-5-6-5-6-5-6-5-6-5-6-7-8) and hPUF_MT(1-2-5-6-5-6-5-6-5-6-5-6-5-6-7-8).

(2) Protein Expression and Purification

Protein expression and purification were performed by the same procedures as in Example 1.

-   Note that protein expression induction was carried out under the     following conditions. -   hPUF_MT(1-2-5-6-5-6-5-6-5-6-5-6-7-8): 37° C. for 3 h in a 1 mM     IPTG-containing LB-Kan medium -   hPUF_MT(1-2-5-6-5-6-5-6-5-6-5-6-5-6-7-8): 37° C. for 3 h in a 1 mM     IPTG-containing LB-Kan medium -   Rotoring for absorption to the resin was carried out for 16 h.

(3) Gel Shift Assay

Gel shift assay was performed by the same procedures as in Example 1.

-   The following RNA probes were used.

OTS-1844: (SEQ ID NO: 35) 5′-Alexa680-CCAGAAUUGUAUAUAUAUUCG-Alexa680-3′ (21 mer) (probe for hPUF_MT(1-2-5-6-5-6-5-6-7-8)) OTS-1925: (SEQ ID NO: 38) 5′-Alexa680-CCAGAAUUGUAUAUAUAUAUAUUCG-Alexa680-3′ (25 mer) (probe for hPUF_MT(1-2-5-6-5-6-5-6-5-6-7-8)) OTS-1926: (SEQ ID NO: 39) 5′-Alexa680-CCAGAAUUGUAUAUAUAUAUAUAUUCG-Alexa680-3′ (27 mer) (probe for hPUF_MT(1-2-5-6-5-6-5-6-5-6-5-6-7-8))

FIG. 35 shows the results.

Example 4 Alteration of Recognition Specificity Example 4-1 (1) Vector Cloning

FIGS. 36 and 37 show the amino acid sequences of hPUF_MT(R3→R5, R4→R5), hPUF_MT(R3→R5→C12N, R4→R5_C12N, R5_C12N), hPUF_MT(R3→R5_C12S, Q16E, R4→R5_C12S, Q16E, R5_C12S, Q16E), and hPUF_MT(R3→R5_C12S, Q16R, R4→R5_C12S, Q16R, R5_C12S, Q16R).

Vector cloning was performed by the same procedures as in Example 2-1.

(2) Protein Expression and Purification

hPUF_MT(R3→R5, R4→R5) is as described above.

Protein expression and purification of hPUF_MT(R3→R5_C12N, R4→R5_C12N, R5_C12N), hPUF_MT(R3→R5_C12S, Q16E, R4 R5_C12S, Q16E, R5_C12S, Q16E), and hPUF_MT(R3→R5_C12S, Q16R, R4→R5_C12S, Q16R, R5_C12S, Q16R) were performed by the same procedures as in Example 1. Note that protein expression induction was carried out under the following conditions.

-   hPUF_MT(R3→R5_C12N, R4→R5_C12N, R5_C12N): 37° C. for 3 h in a 1 mM     IPTG-containing LB-Kan medium -   hPUF_MT(R3→R5_C12S, Q16E, R4→R5_C12N, Q16E, R5_C12S, Q16E): 37° C.     for 3 h in a 0.01 mM IPTG-containing LB-Kan medium -   hPUF_MT(R3→R5_C12S, Q16R, R4→R5_C12N, Q16R, R5_C12S, Q16R): 20° C.     for 24 h in a 1 mM IPTG-containing LB-Kan medium -   Rotoring for absorption to the resin was carried out for 12.5 h.

(3) Gel Shift Assay

Gel shift assay was performed by the same procedures as in Example 1.

The following RNA probe was used.

OTS-1511: (SEQ ID NO: 30) 5′-Alexa680-CCAGAAUUGUAUAUAUUCG-Alexa680-3′ (19 mer) (wild-type sequence) OTS-1841: (SEQ ID NO: 40) 5′-Alexa680-CCAGAAUUGUUUUUAUUCG-Alexa680-3′ (19 mer) (A→U sequence) OTS-1842: (SEQ ID NO: 41) 5′-Alexa680-CCAGAAUUGUGGGUAUUCG-Alexa680-3′ (19 mer) (A→G sequence) OTS-1843: (SEQ ID NO: 42) 5′-Alexa680-CCAGAAUUGUCCCUAUUCG-Alexa680-3′ (19 mer) (A→C sequence)

FIG. 38 shows the results. C12N⋅C12S, Q16E⋅C12S, and Q16R were found to have binding ability greater than that of MT(R3→R5, R4→R5). It is understood that the degree of the binding force is in the following order: C12N (U recognition)>C12S, Q16E (G recognition)>C12S, Q16R (C recognition)>MT (R3→R5, R4→R5) (A recognition).

Example 4-2

The same protein as in Example 4-1 was used.

Gel shift assay was performed by the same procedures as in Example 1.

-   The following RNA probes were used.

OTS-1511: (SEQ ID NO: 30) 5′-Alexa680-CCAGAAUUGUAUAUAUUCG-Alexa680-3′ (19 mer) (wild-type sequence) OTS-1841: (SEQ ID NO: 40) 5′-Alexa680-CCAGAAUUGUUUUUAUUCG-Alexa680-3′ (19 mer) (A→U sequence) OTS-1842: (SEQ ID NO: 41) 5′-Alexa680-CCAGAAUUGUGGGUAUUCG-Alexa680-3′ (19 mer) (A→G sequence) OTS-1843: (SEQ ID NO: 42) 5′-Alexa680-CCAGAAUUGUCCCUAUUCG-Alexa680-3′ (19 mer) (A→C sequence)

FIG. 39 shows the results. Each protein binds only to its target sequence and may have specificity.

Example 4-3 (1) Vector Cloning

FIGS. 40 and 41 show the amino acid sequences of hPUF_MT(R4→R6), hPUF_MT(R4→R6_N12C, R6_N12C), hPUF_MT(R4→R6_N12S, Q16E, R6_N12S, Q16E), and hPUF_MT(R4→R6_N12S, Q16R, R6_N12S, Q16R).

Vector cloning was performed by the same procedures as in Example 2-1.

(2) Protein Expression and Purification

hPUF_MT(R4→R6) is as described above.

Protein expression and purification of hPUF_MT(R4→R6_N12C, R6_N12C), hPUF_MT(R4→R6_N12S, Q16E, R6_N12S, Q16E), and hPUF_MT(R4→R6_N12S, Q16R, R6_N12S, Q16R) were performed by the same procedures as in Example 1. Note that protein expression induction was carried out under the following conditions.

-   hPUF_MT(R4→R6_N12C, R6_N12C): 30° C. for 7 h in a 0.1 mM     IPTG-containing LB-Kan medium -   hPUF_MT(R4→R6_N12S, Q16E, R6_N12S, Q16E): 25° C. for 22 h in a 0.1     mM IPTG-containing LB-Kan medium -   hPUF_MT(R4→R6_N12S, Q16R, R6_N12S, Q16R): 30° C. for 7 h in a 0.1 mM     IPTG-containing LB-Kan medium -   Rotoring for absorption to the resin was carried out for 12 h.

(3) Gel Shift Assay

Gel shift assay was performed by the same procedures as in Example 1.

-   The following RNA probes were used.

OTS-1511: (SEQ ID NO: 30) 5′-Alexa680-CCAGAAUUGUAUAUAUUCG-Alexa680-3′ (19 mer) (wild-type sequence) OTS-1819: (SEQ ID NO: 43) 5′-Alexa680-CCAGAAUUGAAAAUAUUCG-Alexa680-3′ (19 mer) (U→A sequence) OTS-1978: (SEQ ID NO: 44) 5′-Alexa680-CCAGAAUUGGAGAUAUUCG-Alexa680-3′ (19 mer) (U→G sequence) OTS-1979: (SEQ ID NO: 45) 5′-Alexa680-CCAGAAUUGCACAUAUUCG-Alexa680-3′ (19 mer) (U→C sequence)

FIG. 42 shows the results. In the cases of G recognition and C recognition, binding force was almost comparable to or relatively weaker than that of the wild type in the case of U recognition. In the case of A recognition, binding force significantly declined (to about 1/100).

Example 4-4

The same proteins as in Example 4-3 were used.

Gel shift assay was performed by the same procedures as in Example 1. The following RNA probes were used.

OTS-1511: (SEQ ID NO: 30) 5′-Alexa680-CCAGAAUUGUAUAUAUUCG-Alexa680-3′ (19 mer) (wild-type sequence) OTS-1819: (SEQ ID NO: 43) 5′-Alexa680-CCAGAAUUGAAAAUAUUCG-Alexa680-3′ (19 mer) (U→A sequence) OTS-1978: (SEQ ID NO: 44) 5′-Alexa680-CCAGAAUUGGAGAUAUUCG-Alexa680-3′ (19 mer) (U→G sequence) OTS-1979: (SEQ ID NO: 45) 5′-Alexa680-CCAGAAUUGCACAUAUUCG-Alexa680-3′ (19 mer) (U→C sequence)

FIG. 43 shows the results. The results were the same as in Example 4-3 (reproducibility was confirmed).

Example 5 Optimization of Stacking Amino Acids Example 5-1 (1) Vector Cloning

FIGS. 44 and 45 show the amino acid sequences of hPUF_MT(R5_R13K), hPUF_MT(R6_Y13F), hPUF_MT(R6_Y13H), and hPUF_MT(R6_Y13W).

Vector cloning was performed by the same procedures as in Example 2-1.

(2) Protein Expression and Purification

Protein expression and purification were performed by the same procedures as in Example 1.

-   Note that protein expression induction was carried out under the     following conditions. -   hPUF_MT(R5_13K): 37° C. for 3 h in a 0.1 mM IPTG-containing LB-Kan     medium -   hPUF_MT(R6_13F): 37° C. for 3 h in a 0.1 mM IPTG-containing LB-Kan     medium -   hPUF_MT(R6_13H): 37° C. for 3 h in a 0.1 mM IPTG-containing LB-Kan     medium -   hPUF_MT(R6_13W): 37° C. for 3 h in a 0.1 mM IPTG-containing LB-Kan     medium -   Rotoring for absorption to the resin was carried out for 8 h.

(2) Gel Shift Assay

Gel shift assay was performed by the same procedures as in Example 1.

-   The following RNA probe was used.

OTS-1511: (SEQ ID NO: 30) 5′-Alexa680-CCAGAAUUGUAUAUAUUCG-Alexa680-3′ (19 mer)

FIG. 46 shows the results. Arg was the optimal amino acid as a cationic amino acid between A and U (A-U), and Tyr was the optimal amino acid as an aromatic amino acid between U and A (U-A).

Example 5-2 (1) Vector Cloning

FIGS. 47 to 49 show the amino acid sequences of hPUF_MT(R3→R5, R4→R5), hPUF_MT(R3→R5, R4→R5_R13H, R5_R13H), hPUF_MT(R3→R5, R4→R5_R13Y, R5_R13Y), hPUF_MT(R3→R5, R4→R5_R13Y, R5_R13Y), and hPUF_MT(R3→R5, R4→R5_R13W, R5_R13W).

Vector cloning was performed by the same procedures as in Example 2-1.

(2) Protein Expression and Purification

hPUF_MT(R3→R5, R4→R5) is as described above. Protein expression and purification of hPUF_MT(R3→R5, R4→R5_R13H, R5_R13H), hPUF_MT(R3→R5, R4→R5_R13Y, R5_R13Y), hPUF_MT(R3→R5, R4→R5_R13Y, R5_R13Y), and hPUF_MT(R3→R5, R4→R5_R13W, R5_R13W) were performed by the same procedures as in Example 1. Note that protein expression was induced in a 1 mM IPTG-containing LB-Kan medium at 37° C. for 3 h.

-   Rotoring for absorption to the resin was carried out for 3 h.

(3) Gel Shift Assay

Gel shift assay was performed by the same procedures as in Example 1.

-   The following RNA probe was used.

OTS-1759: (SEQ ID NO: 31) 5′-Alexa680-CCAGAAUUGUAAAUAUUCG-Alexa680-3′ (19 mer)

FIG. 50 shows the results. The degree of binding force of a stacking amino acid between A and A (A-A) appears to be Trp>Tyr>>Phe>His.

Example 5-3 (1) Vector Cloning

FIG. 51 shows the amino acid sequence of hPUF_MT(R3→R5, R4→R5_R13K, R5_R13K).

Vector cloning was performed by the same procedures as in Example 2-1.

(2) Protein Expression and Purification

Protein expression and purification were performed by the same procedures as in Example 1.

Note that protein expression was induced in a 0.1 mM IPTG-containing LB-Kan medium at 30° C. for 7 h.

-   Rotoring for absorption to the resin was carried out for 16 h.

(3) Gel Shift Assay

Gel shift assay was performed by the same procedures as in Example 1.

-   The following RNA probe was used.

OTS-1759: (SEQ ID NO: 31) 5′-Alexa680-CCAGAAUUGUAAAUAUUCG-Alexa680-3′ (19 mer)

FIG. 52 shows the results. As the A-A stacking amino acid, aromatic amino acids have stronger binding force than cationic amino acids. Among aromatic amino acids, His and Tyr have high levels of binding force.

Example 5-4 (1) Vector Cloning

FIGS. 53 and 54 show the amino acid sequences of hPUF_MT(R5:A_13R)₃(R6:C_13Y)₃, hPUF_MT(R5:A_13R)₃(R6:C_13R)₃, and hPUF_MT(R5:A_13R)(R5:A_13Y)₂(R6:C_13Y)₃.

Vector cloning was performed by the same procedures as in Example 2-1.

(2) Protein Expression and Purification

Gel shift assay was performed by the same procedures as in Example 1.

Rotoring for absorption to the resin was carried out for 11 h.

(3) Gel Shift Assay

Gel shift assay was performed by the same procedures as in Example 1.

-   The following RNA probe was used.

OTS-2004: (SEQ ID NO: 46) 5′-Alexa680-CCAGAAUUGCACACAUAUUCG-Alexa680-3′ (21 mer)

FIG. 55 shows the results.

When comparing circled numbers 1 and 2, the circled number 1 has about three times greater binding force (Tyr>Arg).

When comparing circled numbers 1 and 3, the circled number 1 has about ten times greater binding force (Arg>Tyr).

Tyr is an appropriate aromatic amino acid between C and A (C-A), and Arg is an appropriate cationic amino acid between A and C (A-C).

Example 5-5 (1) Vector Cloning

FIGS. 56 and 57 show the amino acid sequences of hPUF_MT(R5:A_13R)₃(R6:G_13Y)₃, hPUF_MT(R5:A_13R)₃(R6:G_13R)₃, and hPUF_MT(R5:A_13R)(R5:A_13Y)₂(R6:G_13Y)₃.

Vector cloning was performed by the same procedures as in Example 2-1.

(2) Protein Expression and Purification

Protein expression and purification were performed by the same procedures as in Example 1.

-   Rotoring for absorption to the resin was carried out for 11 h.

(3) Gel Shift Assay

Gel shift assay was performed by the same procedures as in Example 1.

-   The following RNA probe was used.

OTS-2008: (SEQ ID NO: 47) 5′-Alexa680-CCAGAAUUGGAGAGAUAUUCG-Alexa680-3′ (21 mer)

FIG. 58 shows the results.

When comparing circled numbers 1 and 2, the circled number 1 has at least 30 times greater binding force (Tyr>Arg).

-   Tyr is an appropriate aromatic amino acid between G and A (G-A).

When comparing circled numbers 1 and 3, the circled number 1 has slightly greater binding force (Arg>Tyr). Arg is an appropriate cationic amino acid between A and G (A-G).

Example 5-6 (1) Vector Cloning

FIGS. 59 and 60 show the amino acid sequences of hPUF_MT(R5:G_13R)₃(R6:U_13Y)₃, hPUF_MT(R5:G_13R)₃(R6:U_13R)₃, and hPUF_MT(R5:A_13R)(R5:A_13Y)₂(R6:G_13Y)₃.

Vector cloning was performed by the same procedures as in Example 2-1.

(2) Protein Expression and Purification

Gel shift assay was performed by the same procedures as in Example 1.

Rotoring for absorption to the resin was carried out for 11 h.

(3) Gel Shift Assay

Gel shift assay was performed by the same procedures as in Example 1.

-   The following RNA probe was used.

OTS-2004: (SEQ ID NO: 46) 5′-Alexa680-CCAGAAUUGUGUGUGUAUUCG-Alexa680-3′ (21 mer)

FIG. 61 shows the results. When comparing circled numbers 1 and 2, the circled number 2 has about 3 times greater binding force (Tyr>Arg). When comparing circled numbers 1 and 3, the circled number 1 has about 30 times greater binding force (Arg>Tyr). Arg is an appropriate cationic amino acid between U and G (U-G), and Arg is also an appropriate cationic amino acid between G and U (G-U).

Example 6 Comparison with Pumby (1) Vector Cloning

FIGS. 62 and 63 show the amino acid sequences of hPUF_MT(5_(6)8), MT(6_(56)4), and MT(4_(56)4).

Total synthesis of genes encoding hPUF_MT(5(6)₈), MT(6_(56)₄), and MT(4_(56)₄) was carried out. Synthesized genes were cleaved with EcoRI and HindIII and ligated with pET24-R1′-MSC-R8′ which was also cleaved with EcoRI and HindIII, thereby constructing expression vectors. R1′ and R8′ were removed from the constructed expression vectors.

(2) Protein Expression and Purification

Gel shift assay was performed by the same procedures as in Example 1. Note that protein expression was induced in a 1 mM IPTG-containing LB-Kan medium at 37° C. for 3 h.

-   hPUF_MT(5_(5)₈): 20° C. for 21 h in a 0.1 mM IPTG-containing LB-Kan     medium -   hPUF_MT(6_(56)₄): 37° C. for 3 h in a 0.1 mM IPTG-containing LB-Kan     medium -   hPUF_MT(4_(56)₄): 37° C. for 3 h in a 0.1 mM IPTG-containing LB-Kan     medium -   Rotoring for absorption to the resin was carried out for 11 h.

(3) Gel Shift Assay

Gel shift assay was performed by the same procedures as in Example 1.

The following RNA probe was used.

OTS-1511:  (SEQ ID NO: 30) 5′-Alexa680-CCAGAAUUGUAUAUAUUCG-Alexa680-3′ (19 mer)

FIG. 64 shows the results.

Example 7 Extension of Recognition Repeats [2] Example 7-1 (1) Vector Cloning

FIGS. 65 to 67 show the amino acid sequences of hPUF_MT(1-2-6-5-6-5-6-7-8), hPUF_MT(1-2-5-5-6-5-6-7-8), and hPUF_MT(1-2-5-6-5-6-6-7-8).

Vector cloning was performed by the same procedures as in Example 2-1.

(2) Protein Expression and Purification

Protein expression and purification were performed by the same procedures as in Example 1.

(3) Gel Shift Assay

Gel shift assay was performed by the same procedures as in Example 1.

FIG. 68 shows the results. The proteins having extended recognition repeats were found to have binding ability about three times greater than that of WT. The proteins having extended recognition repeats (circled numbers 2 to 4 of 9 repeats in FIG. 67) each had almost the same binding ability.

Example 7-2 (1) Vector Cloning

FIGS. 69 to 71 show the amino acid sequences of hPUF_MT(1-2-6-5-6-5-6-7-8), hPUF_MT(1-2-5-5-6-5-6-7-8), and hPUF_MT(1-2-5-6-5-6-6-7-8).

Vector cloning was performed by the same procedures as in Example 2-1.

(2) Protein Expression and Purification

Protein expression and purification were performed by the same procedures as in Example 7-1.

Note that protein expression of hPUF_MT(1-2-6-5-6-5-6-7-8) was induced in a 0.1 mM IPTG-containing LB-Kan medium at 37° C. for 3 h. Rotoring for absorption to the resin was carried out for 10 h. Protein expression of hPUF_MT(1-2-5-5-6-5-6-7-8) was induced in a 1 mM IPTG-containing LB-Kan medium at 37° C. for 3 h. Rotoring for absorption to the resin was carried out for 10 h. Protein expression of hPUF_MT(1-2-5-6-5-6-6-7-8) was induced in a 0.1 mM IPTG-containing LB-Kan medium at 37° C. for 3 h. Rotoring for absorption to the resin was carried out for 10 h.

(3) Gel Shift Assay

Gel shift assay was performed by the same procedures as in Example 7-1.

Note that the following RNA probes were used.

OTS-1511: (SEQ ID NO: 30) 5′-Alexa680-CCAGAAUUGUAUAUAUUCG-Alexa680-3′ (19 mer) (wild-type sequence) OTS-2080: (SEQ ID NO: 48) 5′-Alexa680-CCAGAAUUGUAUAUUAUUCG-Alexa680-3′ (20 mer) (9 repeats (2)) OTS-2081: (SEQ ID NO: 49) 5′-Alexa680-CCAGAAUUGUAUAAUAUUCG-Alexa680-3′ (20 mer) (9 repeats (3)) OTS-2082: (SEQ ID NO: 50) 5′-Alexa680-CCAGAAUUGUUAUAUAUUCG-Alexa680-3′ (20 mer) (9 repeats (4))

FIG. 72 shows the results. The protein having 13 repeats was found to have the highest binding ability. The protein having 11 repeats was found to have the second highest binding ability, which was about three times greater than that of WT. The protein having 15 repeats was found to have binding ability slightly greater than that of WT.

Example 8 Alteration of Recognition Specificity [2] Example 8-1 (1) Vector Cloning

FIGS. 73 to 76 show the amino acid sequences of hPUF_MT(R3→R5, R4→R6), hPUF_MT(R1_S12N, R3→R5, R4→R6), hPUF_MT(R1_Q16E, R3→R5, R4→R6), and hPUF_MT(R1_Q16R, R3→R4→R6).

Vector cloning was performed by the same procedures as in Example 2-1.

(2) Protein Expression and Purification

Protein expression and purification were performed by the same procedures as in Example 1.

Note that the expression of each protein was induced under the following conditions.

-   hPUF_MT(R1_S12N, R3→R5, R4→R6): 30° C. for 7 h in a 0.001 mM     IPTG-containing LB-Kan medium -   hPUF_MT(R1_Q16E, R3→R5, R4→R6): 30° C. for 7 h in a 0.1 mM     IPTG-containing LB-Kan medium -   hPUF_MT(R1_Q16R, R3→R5, R4→R6): 30° C. for 7 h in a 0.1 mM     IPTG-containing LB-Kan medium

Rotoring for absorption to the resin was carried out for 14 h.

(3) Gel Shift Assay

Gel shift assay was performed by the same procedures as in Example 1.

Note that the following RNA probes were used.

OTS-1511: (SEQ ID NO: 30) 5′-Alexa680-CCAGAAUUGUAUAUAUUCG-Alexa680-3′ (19 mer) (wild-type sequence) OTS-2022: (SEQ ID NO: 51) 5′-Alexa680-CCAGAAUUGUAUAUUUUCG-Alexa680-3′ (19 mer) (A→U sequence) OTS-2020: (SEQ ID NO: 52) 5′-Alexa680-CCAGAAUUGUAUAUGUUCG-Alexa680-3′ (19 mer) (A→G sequence) OTS-2021: (SEQ ID NO: 53) 5′-Alexa680-CCAGAAUUGUAUAUCUUCG-Alexa680-3′ (19 mer) (A→C sequence)

The results are as shown in FIG. 77. As is understood from the figures, the proteins having extended recognition repeats were found to have binding ability about three times greater than that of WT. The results confirmed that the degree of the binding force is in the following order: Q16R (C recognition)>Q16E (G recognition)=MT(R3→R5, R4→R5) (A recognition)>S12N (U recognition).

Further, the results of recognition specificity (FIG. 78) confirmed specificity as described below.

-   (1) MT(R3→R5, R4→R5): The degree of the binding force is in the     order of U=C>A>G. -   (2) MT(R1_S12N,R3→R5, R4→R5) (U recognition): The degree of the     binding force is in the order of U>C>>G=A. -   (3) MT(R1_Q16E,R3→R5, R4→R5) (G recognition): The degree of the     binding force is in the order of G>>U=C. -   (3) MT(R1_Q16E,R3→R5, R4→R5) (C recognition): The degree of the     binding force is in the order of C>U>>G>A.

Note that the number in each pair of parentheses corresponds to the relevant circled number in the figures.

Example 8-2 (1) Vector Cloning

FIG. 79 shows the amino acid sequence of hPUF_MT(R3→R5, R4→R6) (=novel backbone).

Vector cloning was performed by the same procedures as in Example 2-1.

(2) Protein Expression and Purification

Protein expression and purification were performed by the same procedures as in Example 8-1.

(3) Gel Shift Assay

Gel shift assay was performed by the same procedures as in Example 8-1.

Note that the following RNA probes were used.

OTS-1511: (SEQ ID NO: 30) 5′-Alexa680-CCAGAAUUGUAUAUAUUCG-Alexa680-3′ (19 mer) (wild-type sequence) OTS-2022: (SEQ ID NO: 51) 5′-Alexa680-CCAGAAUUGUAUAUUUUCG-Alexa680-3′ (19 mer) (A→U sequence) OTS-2020: (SEQ ID NO: 52) 5′-Alexa680-CCAGAAUUGUAUAUGUUCG-Alexa680-3′ (19 mer) (A→G sequence) OTS-2021: (SEQ ID NO: 53) 5′-Alexa680-CCAGAAUUGUAUAUCUUCG-Alexa680-3′ (19 mer) (A→C sequence)

The results are as shown in FIG. 80. As is understood from the figure, since the wild type originally did not have base specificity, it was confirmed that the alteration of the skeleton was not the reason for the results.

In testing, the first and second samples of WT were tagged with MBP. The results indicating lack of specificity were obtained also for the wild type. In this regard, reproducibility of the novel backbone was confirmed for the third and fourth samples of WT.

Example 8-3 (1) Vector Cloning

FIGS. 81 to 85 show the amino acid sequences of hPUF_MT(R3→R5, R4→R6), hPUF_MT(R2_N12C, R3→R5, R4→R6), hPUF_MT(R2_N12S, R3→R5, R4→R6), hPUF_MT(R2_N12S, Q16E, R3→R5, R4→R6), and hPUF_MT(R2_N12S, Q16R, R3→R5, R4→R6).

Vector cloning was performed by the same procedures as in Example 2-1.

(2) Protein Expression and Purification

Protein expression and purification were performed by the same procedures as in Example 8-1.

Note that protein expression induction was carried out under the following conditions.

-   hPUF_MT(R2_N12C, R3→R5, R4→R6): 30° C. for 7 h in a 0.1 mM     IPTG-containing LB-Kan medium -   hPUF_MT(R2_N12S, R3→R5, R4→R6): 30° C. for 7 h in a 0.1 mM     IPTG-containing LB-Kan medium -   hPUF_MT(R2_N12S, Q16E, R3→R5, R4→R6): 30° C. for 7 h in a 0.1 mM     IPTG-containing LB-Kan medium -   hPUF_MT(R2_N12S, Q16R, R3→R5, R4→R6): 30° C. for 7 h in a 0.1 mM     IPTG-containing LB-Kan medium

Rotoring for absorption to the resin was carried out for 12.5 h.

(3) Gel Shift Assay

Gel shift assay was performed by the same procedures as in Example 8-1.

Note that the following RNA probes were used.

OTS-1511: (SEQ ID NO: 30) 5′-Alexa680-CCAGAAUUGUAUAUAUUCG-Alexa680-3′ (19 mer) (wild-type sequence) OTS-2023: (SEQ ID NO: 54) 5′-Alexa680-CCAGAAUUGUAUAAAUUCG-Alexa680-3′ (19 mer) (U→A sequence) OTS-2024: (SEQ ID NO: 55) 5′-Alexa680-CCAGAAUUGUAUAGAUUCG-Alexa680-3′ (19 mer) (U→G sequence) OTS-2025: (SEQ ID NO: 56) 5′-Alexa680-CCAGAAUUGUAUACAUUCG-Alexa680-3′ (19 mer) (U→C sequence)

The results are as shown in FIG. 86. As is understood from the figure, the results confirmed that the binding proteins having the above amino acid sequences which were prepared as above did not have binding ability greater than that of MT(R3→R5, R4→R5) (left side on the figure) which were prepared as described earlier. The results confirmed that the degree of the binding force is in the following order: MT(R3→R5, R4→R5) (U recognition)>N12S, Q16E (G recognition)>N12S, Q16R (C recognition)>S12C (U recognition).

Example 8-4 (1) Vector Cloning

FIGS. 87 to 90 show the amino acid sequences of hPUF_MT(R3→R5, R4→R6), hPUF_MT(R2_N12C, R3→R5, R4→R6), hPUF_MT(R2_N12S, Q16E, R3→R5, R4→R6), and hPUF_MT(R2_N12S, Q16R, R3→R5, R4→R6).

Vector cloning was performed by the same procedures as in Example 2-1.

(2) Protein Expression and Purification

Protein expression and purification were performed by the same procedures as in Example 8-1.

Note that protein expression induction was carried out under the following conditions.

-   hPUF_MT(R2_N12C, R3→R5, R4→R6): 30° C. for 7 h in a 0.1 mM     IPTG-containing LB-Kan medium -   hPUF_MT(R2_N12S, Q16E, R3→R5, R4→R6): 30° C. for 7 h in a 0.1 mM     IPTG-containing LB-Kan medium -   hPUF_MT(R2_N12S, Q16R, R3→R5, R4→R6): 30° C. for 7 h in a 0.1 mM     IPTG-containing LB-Kan medium

Rotoring for absorption to the resin was carried out for 12.5 h.

(3) Gel Shift Assay

Gel shift assay was performed by the same procedures as in Example 8-1.

Note that the following RNA probes were used.

OTS-1511: (SEQ ID NO: 30) 5′-Alexa680-CCAGAAUUGUAUAUAUUCG-Alexa680-3′ (19 mer) (wild-type sequence) OTS-2023: (SEQ ID NO: 54) 5′-Alexa680-CCAGAAUUGUAUAAAUUCG-Alexa680-3′ (19 mer) (U→A sequence) OTS-2024: (SEQ ID NO: 55) 5′-Alexa680-CCAGAAUUGUAUAGAUUCG-Alexa680-3′ (19 mer) (U→G sequence) OTS-2025: (SEQ ID NO: 56) 5′-Alexa680-CCAGAAUUGUAUACAUUCG-Alexa680-3′ (19 mer) (U→C sequence)

The results are as shown in FIG. 91. As is understood from the figure, the following were indicated.

-   (1) MT(R3→R5, R4→R5): The degree of the binding force is in the     order of U>>C. -   (2) MT(R2_S12C, R3→R5, R4→R5) (A recognition): The degree of the     binding force is in the order of A=U=C>>G. -   (3) MT(R2_N12S, Q16E R3→R5, R4→R5) (G recognition): Binding to G     occurred exclusively. -   (4) MT(R2_N12S, Q16R, R3→R5, R4→R5) (C recognition): Binding to C     occurred exclusively.

Circle numbers 1 to 4 in the figure correspond to (1) to (4) above.

Example 8-5 (1) Vector Cloning

FIGS. 92 to 96 show the amino acid sequences of hPUF_MT(R3→R5, R4→R6), hPUF_MT(R7_S12C,E16Q, R3→R5, R4→R6), hPUF_MT(R7_E16Q, R3→R5, R4→R6), hPUF_MT(R7_S12N,E16Q, R3→R5, R4→R6), and hPUF_MT(R7_E16R, R3→R5, R4→R6).

Vector cloning was performed by the same procedures as in Example 2-1.

(2) Protein Expression and Purification

Protein expression and purification were performed by the same procedures as in Example 8-1.

Note that protein expression induction was carried out under the following conditions.

-   hPUF_MT(R7_S12C, E16Q, R3→R5, R4→R6): 37° C. for 3 h in a 1 mM     IPTG-containing LB-Kan medium -   hPUF_MT(R7_E16Q, R3→R5, R4→R6): 37° C. for 3 h in a 1 mM     IPTG-containing LB-Kan medium -   hPUF_MT(R7_S12N, E16Q, R3→R5, R4→R6): 37° C. for 3 h in a 1 mM     IPTG-containing LB-Kan medium -   hPUF_MT(R7_E16R, R3→R5, R4→R6): 37° C. for 3 h in a 1 mM     IPTG-containing LB-Kan medium

Rotoring for absorption to the resin was carried out for 3.5 h.

(3) Gel Shift Assay

Gel shift assay was performed by the same procedures as in Example 8-1.

Note that the following RNA probes were used.

OTS-1511: (SEQ ID NO: 30) 5′-Alexa680-CCAGAAUUGUAUAUAUUCG-Alexa680-3′ (19 mer) (wild-type sequence) OTS-1754: (SEQ ID NO: 33) 5′-Alexa680-CCAGAAUUAUAUAUAUUCG-Alexa680-3′ (19 mer) (G→A sequence) OTS-2032: (SEQ ID NO: 57) 5′-Alexa680-CCAGAAUUUUAUAUAUUCG-Alexa680-3′ (19 mer) (G→U sequence) OTS-2033: (SEQ ID NO: 58) 5′-Alexa680-CCAGAAUUCUAUAUAUUCG-Alexa680-3′ (19 mer) (G→C sequence)

The results are as shown in FIG. 97. As is understood from the figure, the following were indicated.

The binding proteins having the above amino acid sequences which were prepared as above did not have binding ability greater than that of MT(R3→R5, R4→R5).

The results confirmed that the degree of the binding force is in the following order: MT(R3→R5, R4→R5 (G recognition)>MT(R3→R5, R4→R5, R7_S12N, E16Q) (U recognition)>MT(R3→R5, R4→R5, R7_E16R) (C recognition)>MT(R3→R5, R4→R5, R7_S12C, E16Q (A_E16Q)>MT(R3→R5, R4→R5, R7_S12C, E16Q) (A_S12C, E16Q).

Example 8-6 (1) Vector Cloning

FIGS. 98 to 101 show the amino acid sequences of hPUF_MT(R3→R5, R4→R6), hPUF_MT(R7_S12C,E16Q, R3→R5, R4→R6), hPUF_MT(R7_S12N,E16Q, R3→R5, R4→R6), and hPUF_MT(R7_E16R, R3→R5, R4→R6).

Vector cloning was performed by the same procedures as in Example 2-1.

(2) Protein Expression and Purification

Protein expression and purification were performed by the same procedures as in Example 8-1.

Note that protein expression induction was carried out under the following conditions.

-   hPUF_MT(R7_S12C, E16Q, R3→R5, R4→R6): 37° C. for 3 h in a 1 mM     IPTG-containing LB-Kan medium -   hPUF_MT(R7_S12N, E16Q, R3→R5, R4→R6): 37° C. for 3 h in a 1 mM     IPTG-containing LB-Kan medium -   hPUF_MT(R7_E16R, R3→R5, R4→R6): 37° C. for 3 h in a 1 mM     IPTG-containing LB-Kan medium

Rotoring for absorption to the resin was carried out for 3.5 h.

(3) Gel Shift Assay

Gel shift assay was performed by the same procedures as in Example 8-1.

Note that the following RNA probes were used.

OTS-1511: (SEQ ID NO: 30) 5′-Alexa680-CCAGAAUUGUAUAUAUUCG-Alexa680-3′ (19 mer) (wild-type sequence) OTS-1754: (SEQ ID NO: 33) 5′-Alexa680-CCAGAAUUAUAUAUAUUCG-Alexa680-3′ (19 mer) (G→A sequence) OTS-2032: (SEQ ID NO: 57) 5′-Alexa680-CCAGAAUUUUAUAUAUUCG-Alexa680-3′ (19 mer) (G→U sequence) OTS-2033: SEQ ID NO: 58) (5′-Alexa680-CCAGAAUUCUAUAUAUUCG-Alexa680-3′ (19 mer) (G→C sequence)

The results are as shown in FIG. 102. As is understood from the figure, the following were indicated.

-   (1) MT(R3→R5, R4→R5): Binding to G occurred exclusively. -   (2) MT(R3→R5, R4→R5, R7_S12C, E16Q) (A recognition): The degree of     the binding force is in the order of U>C. -   (3) MT(R3→R5, R4→R5, R7_S12N, E16Q) (U recognition): Binding to U     occurred exclusively. -   (4) MT(R3→R5, R4→R5, R7_E16R) (C recognition): Binding to C and U     occurred.

Note that the number in each pair of parentheses corresponds to the relevant circled number in the figure.

Example 8-7 (1) Vector Cloning

FIGS. 103 to 107 show the amino acid sequences of hPUF_MT(R3→R5, R4→R6), hPUF_MT(R8_N12C, R3→R5, R4→R6), hPUF_MT(R8_N12S, R3→R5, R4→R6), hPUF_MT(R8_N12S, Q16E, R3→R5, R4→R6), and hPUF_MT(R8_N12S, Q16R, R3→R5, R4→R6).

Vector cloning was performed by the same procedures as in Example 2-1.

(2) Protein Expression and Purification

Protein expression and purification were performed by the same procedures as in Example 8-1.

Note that protein expression induction was carried out under the following conditions.

-   hPUF_MT(R8_N12C, R3→R5, R4→R6): 37° C. for 3 h in a 0.01 mM     IPTG-containing LB-Kan medium -   hPUF_MT(R8_N12S, R3→R5, R4→R6): 37° C. for 3 h in a 1 mM     IPTG-containing LB-Kan medium -   hPUF_MT(R8_N12S, Q16E, R3→R5, R4→R6): 37° C. for 3 h in a 0.01 mM     IPTG-containing LB-Kan medium -   hPUF_MT(R8_N12S, Q16R, R3→R5, R4→R6): 37° C. for 3 h in a 0.01 mM     IPTG-containing LB-Kan medium

Rotoring for absorption to the resin was carried out for 11 h.

(3) Gel Shift Assay

Gel shift assay was performed by the same procedures as in Example 8-1.

Note that the following RNA probes were used.

OTS-1511: (SEQ ID NO: 30) 5′-Alexa680-CCAGAAUUGUAUAUAUUCG-Alexa680-3′ (19 mer) (wild-type sequence) OTS-1825: (SEQ ID NO: 36) 5′-Alexa680-CCAGAAUAGUAUAUAUUCG-Alexa680-3′ (19 mer) (U→A sequence) OTS-2034: (SEQ ID NO: 59) 5′-Alexa680-CCAGAAUGGUAUAUAUUCG-Alexa680-3′ (19 mer) (U→G sequence) OTS-2035: (SEQ ID NO: 60) 5′-Alexa680-CCAGAAUCGUAUAUAUUCG-Alexa680-3′ (19 mer)(U→C sequence)

The results are as shown in FIG. 108. As is understood from the figure, the following were indicated.

The binding proteins having the above amino acid sequences which were prepared as above did not have binding ability greater than that of MT(R3→R5, R4→R5). The results confirmed that the degree of the binding force is in the following order: MT(R3→R5, R4→R5) (U recognition)>N12S, Q16R (C recognition)>N12S, Q16E (G recognition). No binding was confirmed for S12C (A recognition)=N12S (A recognition).

Example 8-8 (1) Vector Cloning

FIGS. 109 to 112 show the amino acid sequences of hPUF_MT(R3→R5, R4→R6), hPUF_MT(R8_N12C, R3→R5, R4→R6), hPUF_MT(R8_N12S, Q16E, R3→R5, R4→R6), and hPUF_MT(R8_N12S, Q16R, R3→R5, R4→R6).

Vector cloning was performed by the same procedures as in Example 2-1.

(2) Protein Expression and Purification

Protein expression and purification were performed by the same procedures as in Example 8-1.

Note that protein expression induction was carried out under the following conditions.

-   hPUF_MT(R8_N12C, R3→R5, R4→R6): 37° C. for 3 h in a 0.01 mM     IPTG-containing LB-Kan medium -   hPUF_MT(R8_N12S, Q16E, R3→R5, R4→R6): 37° C. for 3 h in a 0.01 mM     IPTG-containing LB-Kan medium -   hPUF_MT(R8_N12S, Q16R, R3→R5, R4→R6): 37° C., 3 h in a 0.01 mM     IPTG-containing LB-Kan medium

Rotoring for absorption to the resin was carried out for 11 h.

(3) Gel Shift Assay

Gel shift assay was performed by the same procedures as in Example 8-1.

Note that the following RNA probes were used.

OTS-1511: (SEQ ID NO: 30) 5′-Alexa680-CCAGAAUUGUAUAUAUUCG-Alexa680-3′ (19 mer) (wild-type sequence) OTS-1825: (SEQ ID NO: 36) 5′-Alexa680-CCAGAAUAGUAUAUAUUCG-Alexa680-3′ (19 mer) (U→A sequence) OTS-2034: (SEQ ID NO: 59) 5′-Alexa680-CCAGAAUGGUAUAUAUUCG-Alexa680-3′ (19 mer) (U→G sequence) OTS-2035: (SEQ ID NO: 60) 5′-Alexa680-CCAGAAUCGUAUAUAUUCG-Alexa680-3′ (19 mer) (U→C sequence)

The results are as shown in FIG. 113. As is understood from the figure, the following were indicated.

-   (1) MT(R3→R5, R4→R5): Binding to U occurred exclusively. -   (2) MT(R3→R5, R4→R5, R8_N12C) (A recognition): No binding occurred. -   (3) MT(R3→R5, R4→R5, R8_N12S, Q16E) (G recognition): Binding to G     occurred exclusively. -   (4) MT(R1_Q16E, R3→R5, R4→R5) (C recognition): The degree of the     binding force is in the order of C>>G>C.

Note that the number in each pair of parentheses corresponds to the relevant circled number in the figure.

Example 9 Optimization of Stacking Amino Acids [2]

The following 16 types of combinations can be considered for the optimization of the confirmed stacking amino acids. In this Example, experiments were conducted on the levels marked with “*” below to confirm the results.

Stacking between different bases (12 types)

Between A-C/Between C-A

Between A-U/Between U-A*

Between G-A/Between A-G

Between U-G/Between G-U

Between C-G/Between G-C*

Between U-C/Between C-U*

Stacking between the same bases (4 types)

Between A-A*

Between G-G*

Between U-U*

Between C-C*

<Verification of Stacking Amino Acids Regarding Stacking Between Different Bases (FIG. 114)> Example 9-1 Between A-U/Between U-A (FIG. 115) (1) Vector Cloning

FIGS. 116 to 118 show the amino acid sequences of hPUF_MT(R5:A_13R)₃(R6:U_13Y)₃, hPUF_MT(R5:A_13R)₃(R6:U_13R)₃, and hPUF_MT(R5:A_13R)(R5:A_13Y)₂(R6:U_13Y)₃.

Vector cloning was performed by the same procedures as in Example 2-1.

(2) Protein Expression and Purification

Protein expression and purification were performed by the same procedures as in Example 1.

Note that protein expression induction was carried out under the following conditions.

-   hPUF_MT(R5:A_13R)₃(R6:U_13Y)₃: 37° C. for 3 h in a 1 mM     IPTG-containing LB-Kan medium

Rotoring for absorption to the resin was carried out for 9.5 h.

-   hPUF_MT(R5:A_13R)₃(R6:U_13R)₃: 30° C. for 7 h in a 0.1 mM     IPTG-containing LB-Kan medium -   hPUF_MT(R5:A_13R)(R5:A_13Y)₂(R6:U_13Y)₃: 37° C. for 3 h in a 1 mM     IPTG-containing LB-Kan medium

Rotoring for absorption to the resin was carried out for 8 h.

(3) Gel Shift Assay

Gel shift assay was performed by the same procedures as in Example 1.

Note that the following RNA probe was used.

OTS-1844: (SEQ ID NO: 35) 5′-Alexa680-CCAGAAUUGUAUAUAUAUUCG-Alexa680-3′  (21 mer)

FIG. 119 shows the results. A comparison of circled numbers 1 and 2 showed that the circled number 1 has at least 30 times greater binding force (Tyr>Arg). A comparison of circled numbers 1 and 3 showed that both the circled numbers 1 and 3 have the equivalent binding force (Arg=Tyr). It was found that there was no significant difference between U-A for Tyr as an aromatic amino acid, and there was no significant difference between A-U for Arg and Tyr.

Example 9-2 Between C-G/Between G-C (FIG. 120) (1) Vector Cloning

FIGS. 121 to 123 show the amino acid sequences of hPUF_MT(R5:G_13R)₃(R6:C_13Y)₃, hPUF_MT(R5:G_13R)₃(R6:C_13R)₃, and hPUF_MT(R5:G_13R)(R5:G_13Y)₂(R6:C_13Y)₃.

Vector cloning was performed by the same procedures as in Example 2-1.

(2) Protein Expression and Purification

Protein expression and purification were performed by the same procedures as in Example 1.

Note that protein expression induction was carried out under the following conditions.

-   hPUF_MT(R5:G_13R)₃(R6:C_13Y)₃: 37° C. for 3 h in a 1 mM     IPTG-containing LB-Kan medium -   hPUF_MT(R5:G_13R)₃(R6:C_13R)₃: 37° C. for 3 h in a 1 mM     IPTG-containing LB-Kan medium -   hPUF_MT(R5:G_13R)(R5:G_13Y)₂(R6:C_13Y)₃: 37° C. for 3 h in a 1 mM     IPTG-containing LB-Kan medium

Rotoring for absorption to the resin was carried out for 12 h.

(3) Gel Shift Assay

Gel shift assay was performed by the same procedures as in Example 1.

Note that the following RNA probe was used.

OTS-2007: (SEQ ID NO: 61) 5′-Alexa680-CCAGAAUUGCGCGCGUAUUCG-Alexa680-3′ (24 mer)

FIG. 124 shows the results. A comparison of circled numbers 1 and 2 showed that the circled number 2 has slightly greater binding force (Tyr<Arg). A comparison of circled numbers 1 and 3 showed that the circled number 1 has slightly greater binding force (Arg>Tyr). It was found that Arg was a suitable cationic amino acid between C-G, and Arg was also a suitable cationic amino acid between G-C.

Example 9-3 Between U-C/Between C-U (FIG. 125) (1) Vector Cloning

FIGS. 126 to 128 show the amino acid sequences of hPUF_MT(R5:C_13R)₃(R6:U_13Y)₃, hPUF_MT(R5:C_13R)₃(R6:U_13R)₃, and hPUF_MT(R5:C_13R)(R5:C_13Y)₂(R6:U_13Y)₃.

Vector cloning was performed by the same procedures as in Example 2-1.

(2) Protein Expression and Purification

Protein expression and purification were performed by the same procedures as in Example 1.

Note that protein expression induction was carried out under the following conditions.

-   hPUF_MT(R5:C_13R)₃(R6:U_13Y)₃: 37° C. for 3 h in a 0.1 mM     IPTG-containing LB-Kan medium -   hPUF_MT(R5:C_13R)₃(R6:U_13R)₃: 37° C. for 3 h in a 0.1 mM     IPTG-containing LB-Kan medium -   hPUF_MT(R5:C_13R)(R5:C_13Y)₂(R6:U_13Y)₃: 37° C. for 3 h in a 0.1 mM     IPTG-containing LB-Kan medium

Rotoring for absorption to the resin was carried out for 13.5 h.

(3) Gel Shift Assay

Gel shift assay was performed by the same procedures as in Example 1.

Note that the following RNA probe was used.

OTS-2006: (SEQ ID NO: 62) 5′-Alexa680-CCAGAAUUGUCUCUCUAUUCG-Alexa680-3′ (21 mer)

FIG. 129 shows the results. A comparison of circled numbers 1 and 2 showed that the circled number 1 has about 10 times greater binding force (Tyr>Arg). A comparison of circled numbers 1 and 3 showed that the circled number 3 has slightly greater binding force (Arg<Tyr). In other words, Tyr was an appropriate aromatic amino acid between U-C, and Tyr is was also an appropriate aromatic amino acid between C-U.

<Verification of Stacking Amino Acids Regarding Stacking Between the Same Bases (FIG. 130)> Example 9-4 Between A-A (FIG. 131) (1) Vector Cloning

FIGS. 132 to 137 show the amino acid sequences of hPUF_MT(R3→R5, R4→R5), hPUF_MT(R3→R5, R4→R5_R13K, R5_R13K), hPUF_MT(R3→R5, R4→R5_R13F, R5_R13F), hPUF_MT(R3→R5, R4→R5_R13H, R5_R13H), hPUF_MT(R3→R5, R4→R5_R13W, R5_R13W), and hPUF_MT(R3→R5, R4→R5_R13Y, R5_R13Y).

Vector cloning was performed by the same procedures as in Example 2-1.

(2) Protein Expression and Purification

Protein expression and purification were performed by the same procedures as in Example 1.

Note that protein expression induction was carried out under the following conditions.

-   hPUF_MT(R3→R5, R4→R5): 30° C. for 7 h in a 0.01 mM IPTG-containing     LB-Kan medium

Rotoring for absorption to the resin was carried out for 10 h.

-   hPUF_MT(R3→R5, R4→R5_R13K, R5_R13K): 30° C. for 7 h in a 0.1 mM     IPTG-containing LB-Kan medium

Rotoring for absorption to the resin was carried out for 16 h.

-   hPUF_MT(R3→R5, R4→R5_R13F, R5_R13F): 37° C. for 3 h in a 1 mM     IPTG-containing LB-Kan medium -   hPUF_MT(R3→R5, R4→R5_R13H, R5_R13H): 37° C. for 3 h in a 1 mM     IPTG-containing LB-Kan medium -   hPUF_MT(R3→R5, R4→R5_R13W, R5_R13W): 37° C. for 3 h in a 1 mM     IPTG-containing LB-Kan medium -   hPUF_MT(R3→R5, R4→R5_R13Y, R5_R13Y): 37° C. for 3 h in a 1 mM     IPTG-containing LB-Kan medium

Rotoring for absorption to the resin was carried out for 3 h.

(3) Gel Shift Assay

Gel shift assay was performed by the same procedures as in Example 1.

Note that the following RNA probe was used.

OTS-1759: (SEQ ID NO: 31) 5′-Alexa680-CCAGAAUUGUAAAUAUUCG-Alexa680-3′ (19 mer)

FIG. 138 shows the results. It was found that aromatic amino acids have greater binding force than that of cationic amino acids. It was found that among aromatic amino acids, His and Tyr have the greatest binding force (H=Y>R>F=W>K).

Example 9-5 Between G-G (FIG. 139) (1) Vector Cloning

FIGS. 140 to 145 show the amino acid sequences of hPUF_MT(R5:G 13R)₃, hPUF_MT(R5:G_13K)₃, hPUF_MT(R5:G_13F)₃, hPUF_MT(R5:G_13H)₃, hPUF_MT(R5:G_13W)₃, and hPUF_MT(R5:G_13Y)₃.

Vector cloning was performed by the same procedures as in Example 2-1.

(2) Protein Expression and Purification

Protein expression and purification were performed by the same procedures as in Example 1.

Note that protein expression induction was carried out under the following conditions.

-   hPUF_MT(R5:G_13R)₃: 37° C. for 3 h in a 0.01 mM IPTG-containing     LB-Kan medium

Rotoring for absorption to the resin was carried out for 12.5 h.

-   hPUF_MT(R5:G_13K)₃: 37° C. for 7 h in a 1 mM IPTG-containing LB-Kan     medium -   hPUF_MT(R5:G_13F)₃: 37° C. for 7 h in a 1 mM IPTG-containing LB-Kan     medium -   hPUF_MT(R5:G_13H)₃: 37° C. for 7 h in a 1 mM IPTG-containing LB-Kan     medium -   hPUF_MT(R5:G_13W)₃: 37° C. for 7 h in a 1 mM IPTG-containing LB-Kan     medium -   hPUF_MT(R5:G_13Y)₃: 37° C. for 7 h in a 1 mM IPTG-containing LB-Kan     medium

Rotoring for absorption to the resin was carried out for 14 h.

(3) Gel Shift Assay

Gel shift assay was performed by the same procedures as in Example 1.

Note that the following RNA probe was used.

OTS-1842: (SEQ ID NO: 41) 5′-Alexa680-CCAGAAUUGUGGGUAUUCG-Alexa680-3′ (19 mer)

FIG. 146 shows the results. It was found that cationic amino acids have greater binding force than that of aromatic amino acids. It was found that among aromatic amino acids, Arg has the greatest binding force (R=H>K>W=Y>F).

Example 9-6 Between U-U (FIG. 147) (1) Vector Cloning

FIGS. 148 to 153 show the amino acid sequences of hPUF_MT(R5:U_13R)₃, hPUF_MT(R5:U_13K)₃, hPUF_MT(R5:U_13F)₃, hPUF_MT(R5:U_13H)₃, hPUF_MT(R5:U_13W)₃, and hPUF_MT(R5:U_13Y)₃.

Vector cloning was performed by the same procedures as in Example 2-1.

(2) Protein Expression and Purification

Protein expression and purification were performed by the same procedures as in Example 1.

Note that protein expression induction was carried out under the following conditions.

-   hPUF_MT(R5:U_13R)₃: 37° C. for 3 h in a 1 mM IPTG-containing LB-Kan     medium

Rotoring for absorption to the resin was carried out for 12.5 h.

-   hPUF_MT(R5:U_13K)₃: 37° C. for 3 h in a 0.1 mM IPTG-containing     LB-Kan medium -   hPUF_MT(R5:U_13F)₃: 37° C. for 3 h in a 1 mM IPTG-containing LB-Kan     medium -   hPUF_MT(R5:U_13H)₃: 37° C. for 3 h in a 0.1 mM IPTG-containing     LB-Kan medium -   hPUF_MT(R5:U_13W)₃: 37° C. for 3 h in a 1 mM IPTG-containing LB-Kan     medium -   hPUF_MT(R5:U_13Y)₃: 37° C. for 3 h in a 1 mM IPTG-containing LB-Kan     medium

Rotoring for absorption to the resin was carried out for 14 h.

(3) Gel Shift Assay

Gel shift assay was performed by the same procedures as in Example 1.

Note that the following RNA probe was used.

OTS-1841: (SEQ ID NO: 40) 5′-Alexa680-CCAGAAUUGUUUUUAUUCG-Alexa680-3′ (19 mer)

FIG. 154 shows the results. It was found that aromatic amino acids have greater binding forth than that of cationic amino acids. It was found that among aromatic amino acids, Trp has the greatest binding force (W=R>H>F=Y>K).

Example 9-7 Between C-C (FIG. 155) (1) Vector Cloning

FIGS. 156 to 161 show the amino acid sequences of hPUF_MT(R5:C_13R)₃, hPUF_MT(R5:C_13K)₃, hPUF_MT(R5:C_13F)₃, hPUF_MT(R5:C_13H)₃, hPUF_MT(R5:C_13W)₃, and hPUF_MT(R5:C_13Y)₃.

Vector cloning was performed by the same procedures as in Example 2-1.

(2) Protein Expression and Purification

Protein expression and purification were performed by the same procedures as in Example 1.

Note that protein expression induction was carried out under the following conditions.

-   hPUF_MT(R5:C_13R)₃: 20° C. for 24 h in a 1 mM IPTG-containing LB-Kan     medium

Rotoring for absorption to the resin was carried out for 12.5 h.

-   hPUF_MT(R5:C_13K)₃: 30° C. for 7 h in a 0.1 mM IPTG-containing     LB-Kan medium -   hPUF_MT(R5:C_13F)₃: 30° C. for 7 h in a 0.1 mM IPTG-containing     LB-Kan medium -   hPUF_MT(R5:C_13H)₃: 30° C. for 7 h in a 0.1 mM IPTG-containing     LB-Kan medium -   hPUF_MT(R5:C_13W)₃: 30° C. for 7 h in a 0.1 mM IPTG-containing     LB-Kan medium -   hPUF_MT(R5:C_13Y)₃: 30° C. for 7 h in a 0.1 mM IPTG-containing     LB-Kan medium

Rotoring for absorption to the resin was carried out for 14 h.

(3) Gel Shift Assay

Gel shift assay was performed by the same procedures as in Example 1.

Note that the following RNA probe was used.

OTS-1843: (SEQ ID NO: 42) 5′-Alexa680-CCAGAAUUGUCCCUAUUCG-Alexa680-3′ (19 mer)

FIG. 162 shows the results. It was found that F is most suitable (F>H>W>R=K>Y). 

I claim:
 1. An RNA-binding protein having an amino acid sequence represented by R1′-R1X-R2X-(R5X or R6Y)_(L)-(R5X-R6Y)_(M)-(R5X or R6Y)_(N)-R7X-R8X-R8′: wherein R1X represents R1, R1(S12N), R1(S12C), R1(Q16E), or R1(Q16R), R2X represents R2, R2(N12C), R2(N12S), R2(N12S, Q16E), or R2(N12S, Q16R), R5X represents any one of R5, R5(C12S), R5(C12N), R5(C12S, Q16E), or R5(C12S, Q16R), R6Y represents any one of R6, R6(N12C), R6(N12S), R6(N12S, Q16E), or R6(N12S, Q16R), R7X represents R7, R7(S12C, E16Q), R7(E16Q), R7(S12N, E16Q), or R7(E16R), R8X represents R8, R8(N12C), R8(N12S), R8(N12S, Q16E), or R8(N12S, Q16R). S12N represents a substitution of a 12th amino acid S with N, S12C represents a substitution of a 12th amino acid S with C, N12C represents a substitution of a 12th amino acid N with C, N125 represents a substitution of a 12th amino acid N with S, C12N represents a substitution of a 12th amino acid C with N, C12S represents a substitution of a 12th amino acid C with S, Q16E represents a substitution of a 16th amino acid Q with E, Q16R represents a substitution of a 16th amino acid Q with R, E16Q represents a substitution of a 16th amino acid E with Q, E16R represents a substitution of a 16th amino acid E with R, L and N each independently represent 0 or 1, and M represents an integer of 2 or more, M preferably represents an integer of 2 to 20, more preferably an integer of 2 to 10, and even more preferably an integer of 2 to 5, and each repeat corresponds to the following relevant amino acid sequence: R1′: (SEQ ID NO: 9) GRSRLLEDFRNNRYPNLQLREIAG; R1: (SEQ ID NO: 1) HIMEFSQDQHGSRFIQLKLERATPAERQLVFNEILQ; R2: (SEQ ID NO: 2) AAYQLMVDVFGNYVIQKFFEFGSLEQKLALAERIRG; R5: (SEQ ID NO: 5) QVFALSTHPYGCRVIQRILEHCLPDQTLPILEELHQ; R6: (SEQ ID NO: 6) HTEQLVQDQYGNYVIQHVLEHGRPEDKSKIVAEIRG; R7: (SEQ ID NO: 7) NVLVLSQHKFASNVVEKCVTHASRTERAVLIDEVCTMNDGPHS; R8: (SEQ ID NO: 8) ALYTMMKDQYANYVVQKMIDVAEPGQRKIVMHKIRP; R8′: (SEQ ID NO: 10) HIATLRKYTYGKHILAKLEKYYMKNGVDLG,

wherein for at least one of the repeats R1X, R2X R5X R6Y, R7X, and R8X, in a case in which a combination of a base recognized by the repeat and a downstream base adjacent thereto is A-A, the 13th amino acid of the corresponding repeat (i.e., an amino acid stacking between the two bases) is Tyr or His, in a case in which the combination is G-A, U-A, C-A, U-C, or C-U, the 13th amino acid of the corresponding repeat (i.e., an amino acid stacking between the two bases) is Tyr, in a case in which the combination is A-G, A-C, G-U, U-G, C-G, or G-C, the 13th amino acid of the corresponding repeat (i.e., an amino acid stacking between the two bases) is Arg, in a case in which the combination is A-U or G-G, the 13th amino acid of the corresponding repeat (i.e., an amino acid stacking between the two bases) is Arg or His, in a case in which the combination is U-U, the 13th amino acid of the corresponding repeat (i.e., an amino acid stacking between the two bases) is Trp or Arg, and/or in a case in which the combination is C-C, the 13th amino acid of the corresponding repeat (i.e., an amino acid stacking between the two bases) is Phe.
 2. A nucleic acid encoding the RNA-binding protein according to claim
 1. 3. A recombinant expression vector including the nucleic acid according to claim
 2. 4. A host cell including the recombinant expression vector according to claim
 3. 